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51:6:‘1 .; P.:..&r¢3;-r‘€k~.i

OF SOME WEAK ACIDS IN NON-AQUEOUS

MEDEA

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Thesis 5%» fhe Degree of M. S.

fliECHEGAN STATE *JNNERSE'FY

Ray Haoser

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HIGH FREQUENCY TITRATION OF SOME km ACIDS

IN NON-AQUECIJS MEDIA

By

Ray Hooser

A THESIS

Submitted in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Chemistry

Michigan State University

East Lansing, Michigan

1956

ACKNWLEDCHENTS

The enthor it greatly iniabted to Dr. Andrew Tinnick

whole kindnes- nnd petient supervision node the completion

of thin investigation possible.

Grateful acknowledment in also due to Dr. K. G. 'Stone

and Dr. W, 1‘. Lippincott for helpful enggeetione, end to

Hr. D. 1. Column for his timely “listen“.

HIM FREQUEXCI TURBIOI N SHE max ACIDS

IN NCI~AQUEOUS MEDIA

By

Rey Hoocer

AN ABSTRACT

knitted in Mid fulfillnent of the requiremente

for the degree or

MASTER OF SCIENCE

Department of Ghenietry

Ieer 1956

‘Ppmed 4W.—

iii

ABSTRACT

A grid-dip, capeoitetive type high frequency titretion epperetue

opereting et lhl ”peyolee we need to deter-me ehether high frequency

titretione of week eoide in eprotio' or baeio eolvente ere practioel end

whether the neth offere eny edvantagee over potentionetric or indiv-

eeter nethode of enelyeie for these solvent eyetene.

Sueoeeeful high frequency titretione of n-uinobeneoio, beneoie,

nelenie, g-nitrobeneoio, end ealioylio wide were perfor-ed in beneene-

lethenel lined eolvent ei'th‘poteeeiun nethoxide in beneene-nethenel.

lo euooeeeful high frequency titretione of oeteohol, hydroquinone,

phenol, or reeoroinol were eooonpliehed enploying thie eolvent-titrut

ml.

Reeeoetophenone , B-quinolinol , 2 ,h ,6—triohlorophenol, or nnillin

were moeeefully titrated in dinothylfomaldde with poteeeiun nethezlde

in heneene-nethanol. The end point breelce for benzoio eoid, salicylio

eeid, er lethyl eelioylete ranged from poorly defined to indeterlinete.

lo euoeeeefel high frequency titretione of phenol or outeehol were

eoeomliehed employing this eolvent-titrent eyeten .

High frequency titretione of very weak eoide in dinethylforlenide

with dooholio poteeeim hydroxide titrent proved euooeeeful for the

Ienohydroq phenole , B—beneylphenol, Bohronophenol , g-Mroxydiphenyl,

29mphthol, end phenol. The end point breeke for g-tert-emylplmnel

were eherp but the reeulte are very erratic. High frequency titretion

iv

I

- e e

M .

.

q

. . .

I

.-

a

F‘ n

e 1 , .

, .

' .

‘ ' .u

. ; , . ..

~ ‘ ,9

- , -

e - e e ‘ ' |

.

Z

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.

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..

. ov - - 4

f < ,' |

e

s

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. A

- 5

—-

- e

e

of ceteohol or phloroglucinol were unneeeeeful, poeeibly beoeuee of

exidetion in emcee beeio titrant.

High frequency titretione of edipic eoid , ruinobeneoie , beneoio

eeid, ethnic eoid, methyl eelioylete, g—nitrobeneodo eoid, B-quinolinol,

"WW”, 2);,6-trlohlorophenol, or vanilla in dilethyflormemide

were performed eucoeeefully with alcoholic: poteeeiun' hydroxide titrent.

' Although comparable titretion reeulte m obteined for the di-

Iethylferlenide eolvent eyeten by high frequency end potentiuetrio

sewage» high frequency nethed 1- lore ecu-«nu einee the electrodes

do not eeee inte mm uith the anthem. titreted. By a... high

frequency method verym eoide were eunuch: dinetlvlfornanide.

Such titretione he" not been emied out euooeeefully by en indioeter

lethal. l t

TABLE CE" cmms

Pep

mmmeIOOOOCOOOOCC0.000...0.0.0.0...OOOOOIOOOOOODOOOOOIOOO

Emma lmmeDOOOOCQOOOOOOCO00......IOIOCOOOOOOOOOOOICC...

Hon-191100” witMtryeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

High Fflqmmy 'mqm Titrmtneeeeeeeeeeeeeeeeeeeeeeeee

mmuCCOOOOOOOCOCOCOOCDOC...0.0.0.0....‘IOOUOOOOOOOOOOOOO.

R“FWOQOCOOIOOOOOIIOOOOOOOOOOOOIODIOOOUIOOOOIO09.00.0000...

Wt”....QCOOO-OOOOOIOOOOOO0.0.0....OOOOOOOOIOOQOOOO0......

Titration mama...OOOOCIOOQOOCOOOO0.00000IOOOOOOOCOOOO...

vumIOOOOOCCI0......00......000.....QCCCCCOOOOOOQOCOICOCCC

PotantimtflcoOOO.00....0...OOIOOCOOOOOOOOOOOO0.0.0.000...

commtmtncl...:COO0.000000CCOO-OOCOOOOOOOOOIOOOI.DIG...

High anmy.00.000.00.000...O'COQOOOIOOOOOOIOOOOO0......

melou a WHSOOOOCOOOOIOOOOOOOQOOIOOOOOCOOIOOQOOOQCOOOOOO

WGW.OOIOOCOOOOOOOOO0.00.0... OCOIOOOOOOOOOOIOOOOOI.

Titretione in Demon-Methanol Solvent (Potueiun Motheride u

Titr‘nt 0.00.....OOOOOIOOOOOOOCOOOOOOOOOOOOOOQOOO0.00......

High heqmmy...i...I.O000....COCOOQCOOCOOO‘C'OOCCCOCOOCOOOC

Titratione in Dinetlvlfornenide Solvent (Poteeeiue Methoxide

“ Titmt 00......OOOOOIOOOOOOOQ‘OOOOOOOOOOIOOCOOQOOOI0....

omdue‘mtfloOOOOOOOOOIOOOO0.00.00.00.00000000COOOOOOIO...

PauntimtfloOOOOI.0.0.0.0....OQOOCOOOOOOOOIIOO.OOVOOCCOOO

mgh qummy...OOCCCOCCCUOCOOCOCOCI .COOOCCOOOCDOCOCOCOCO

Titretione in Dinethylforlmide Solvent (Alcoholic Poteeeiml

Wfldo ” Tim)0......OOOOOOOOOOO.COCOOOOOOICCOOOOOOO

Pountim00000.0000000000......CC.OIOOOOOOOOCOOOOOQOOOO

men FNWBWOOOOOOOOO00......000000 O‘COOOOOOOOOOCOOOOOOO

Titretione in Dimtmrlformmide Solvent Sodilnu Hothoadde u

Titr‘nt)OOOOCOOOOOOO‘OOOOOOOOOCOD...QIOOOOOOOOOOOUOOOOOO...

V1MCOIOOOOOOO.OOOOOOI00......I..(OOIOOOOOOODOOOOOOOOOOOI

Ititratione in Ethylenedianine Solvent Sodium Hethoxide ee

Titr‘nt DOOOOOOQIDOIOODO0.0COOOOOOOOOOOOOOOOCOOOOOOOCIOOOOO

VMOOOOOIOOOCDOOOOOIOOOOOOOOOOOOOOOOOOCOOOQOOOOOO0......

Tmtion or Titration RomuOOOOI‘OOOOOOOOOOOO0.0.0.0000...

'Uneetiefeotory Solvent System for High Frequency Titrimetry..

m“D cmmmOIOOOOOOOOOOOCOOOO0......OOOIOOOOOOOOOOIOOOOO

mm: OHEOOOOCOOIOOIUOOOOOOOOOOOIOOOCOOOOCOCOOOOOOOOOOOOOO

vi

pPEUSSfia

como

Mp O~

LIST OF TABLES

rm Page

I Titratione of Very heck icicleeeepqeeeeeeeeeeeeeeeeeeeeeeee 38

II Titratione of Week AcidsOOOOOCOCICOOOOOOOOOO0......0...... ‘41

vii

LIST w FIGURES

FICKIRE Page

1. Reepome Curvee for Potaeeim Methcdde, et Varioue

’flqmi°.eeeeeeeeoeeoeeeeeeeeeeeeeéeeeeeeeeeeeeeeeeeeeeeee 18

20 mm. cm.eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 19

3. Reeponee Curve for Alcoholic Poteeeim Hydroxide............ 20

1;. High Frequency Titretion Curvee for Week Acide in Bemene-

Hethenol, Potassium Hethoxide Titrent....................... 21

5. High Frequency Titration Curves for Week Acide in Benzene-

”W, ijou Kama.Titrmtee‘eeeeeeeeeeeeeeeeeeeee 22

6. High Frequency end Conductintric Titretion Curvee for

Domain “idOCOOOOOCOOOOOCUOOOOOOOOO...00......000.000.00.00 21‘

7. High Frequency Titration Curves for Week lcide in Dinethyl-

fornenide, Poteeeiun Hethoxide Titrent...................... 25

8. CMI n.0‘m PufOWQOOOOCIOOOO.‘IOOOOOOQOOOOO...O... 2?

9 . Potenticnetric Titration Curvee for Vericue Phenole in

Dilethylfornenide Titretcd with Alcoholic Potceeiun

I.mz'O‘Id.eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 28

lo. High Frequency fitreticn‘ Curvee for Very Week icide in

Dinetkqlfornnnide , Alcoholic Poteeeiun Hydroxide Titrent. . . . 30

11. High Frequency Titration Curvee for Very Weak Acids in

Dinethylfornenide, Alcoholic Poteeeiun Hydroxide Iitrent.... 31

12. High Frequency titration Curves for Week Acide in Dieethyle

fornuide, Alcoholic Poteeeiun Hydroxide Titrant............ 32

13. High Frequency Titreticn Curvee for Week Acide in Dimethyl-

, fer-elude, Alcoholic Potaeeiun Hydronde Titrant............ 33

in. High Frequency Titration Curvee for Week icide in Dimothyl-

fornmide , Alcoholic Poteeeiun Hydroxide Titrant............ 3h

15. High Frequency Titration Curve for e Hitture of Phenol end

2A’6-Tr1cmmphan01000000.00.00...OOOOOOOOO...0.0.0.000... 36

viii

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. Q'I

INTRODUCTION

High frequency titretione ere purported to offer two dietinct

edventegee over potentiometric titration: in non-equecue eyetenet

l) the electrode ere not in contect with the eolution, thereby clini-

ueting the eerioue problem of electrode deactivation and liquid-

junction irreguhritiee end , 2) measurenente. necrothe equivelence point

have no epoch]. eignificence. The end point ie doternined by the

interaction of the extrapoleted straight line portione of the titration

curve on either eide of the end point where the enceee of the ion being

titrated er the emcee of the titrent will repreee the hydrolyeie,

eclubility, or dieeocietion of the reaction produote.

i nejor footer for the limited acceptance of high frequency

titretien nethode bee heen the he]: of e eteble, eeneitive , reletieely

eilple inetrunent cepeble of operating in the negaoycle region. Within

the loot you, nowdcll, g_t_ g... (h) and Johneon and Tinnick (23).heve

reported the developlent of einple , eteble inetrunente which poeeeee

the deeired eeneitivity for both equeoue end non-aqueoue titrinetry.

Llpplncott end emick (26) heve found thet the inetrlenent developed

by Johnecn end finnick gen excellent reeulte for the titration of not,

eebetituted enilinee in glacial ecetic acid eolvent with perchloric

eoid in gleciel eeetic ecid. Therefore , this investigation wee under-

telcen to deter-inc: 1) if high frequency titretione of week ecide in

tprctio or beeic eolvente ere precticel end, 2) 1: the method offere cw

edventegee over potentiometric or vieuel methods for theee eolvent eyetene.

HISTORICAL BEKCRQIND

Ion—aqueoue Titrimetr;

Folio end Wentwrth (5) in 1910 carried out the am enelytioel

non-eqnewe titretione with the titration of eome higher fatty ecide

in nriouo eprotio eolvente with sodium elooholete, neing phenol-

phthelein es the iniioetor .

Although lone work all done efter this, the field lenguiehed until

hrfuted, Lory, end Lode fornuleted their eoid-beee theoriee, thee

putting mn-equeoue titrieetry on a more firm theorioel belie.

The next senor edmoeuent we the etudy of 'euper wide" by

Iell, Genent end Werner (1,16,17) in which they reported titretione of

ink been in gleoiel eoetio acid medium eith etrong mineral eoide.

The firet non-eqneoue eoid—beee titretion to find wide eooeptenoe

he the procedure of ledeen end Brenchen (28) for the deteminetion of

nine aide in mtio eoid with perchlorio ecid in ghoul eoetio eeid.

loee, Elliott, end Hell (27) reported the euooeeefnl titretion of

phenol end other very weak eoide in ethylenodianine with eodime mino-

ethozide in the Isle eolvent .

Ion-queue titrinetry came into proninenoe with the recent,

repid expenlion of the ohenioel end phereeoentioel induetriee. Nunemne,

repid oontrol prooeduree for my organic interlediete and fine]. prodnote

Ihioh ere too week on eoide and beeoe to be determined in eqneone sedit-

hed to be developed. 1 major ehere of the oredit for developing tbie

field mt be given to Fritz (6-15). Riddiok (31.,35), Wollieh end Pifer

(30.31.32) .

All four types of eolvents, basic, ecidic, mphiprotic, eni

We, here been utilized in non-equeous titrinetry (3h,3$). 1').

properties of the compound to be titrated must be considered in the

choice of e suitable solvent. Since a basic solvent will enhance the

apparent ecidity of week acids dissolved in it, ethylonodienine wuld

be e proper choice of. solvent for titratione of ccmpomde such es

phenol, ochroncxphenol, or cetechol. Likewise, en acidic solvent such

es gleciel acetic ecid which enhances the apparent besicity of any

seek beee dissolved in it would be chosen for eniline, g—chloroenfline,

end pyridine. Since there is little or no lmling effect in eprotio

end emphiprotic solvents, they are often selected when differential

titretions of mixtures oonteining coupounde of eubstentielly different

pK'e ere desired. in emplo of this would he the differential ti-

tration of e mixture of phenol, eoetic acid, and hydrochloric ecid

dileolvod in dinethylfornmide with elcoholic potassium hydroxide

titrent (2).

Among the many titrente suggested for use in non-equecul titrimetry,

perchloric ecid in glacial ecetic acid hes been elnoet universally

edopted for titration of week beeee . However, no one titrant hes yet

been found uhichsetiefiee ell the requirements for e good titrent for

week acids. Deel end Wyld'e suggestion of potassium hydroxide dis-

solved in isopropyl elcohol eppears to the best developed thus fer (2).

Other titrente which have been tried are potaseitm nethoxide, sodium

nethcxide, sodium mimethoxide , end tetrebutylemnoniun hydroxide (5 ) .

workers. in non-equeoue titrinetry have been plagued tron the

beginning dth e leak of suiteble means of end point detection.

1-H

Sane specific «indicetore ere eveileble, but no series of indicetors to

cover the entire eo-celled "pH range“ for each solvent system hes yet

been developed (6).

Instrumental eethods of enelysis which have been utilised to

circulwent this difficulty ere potantiometry (6) , photometry (33),

conductimetry (18,19), and high frequency titrinetry (3,20,21,25,26,37) .

or these, potenticnetric titrinetry has received the lost ettention.

as problem ehich hes not yet been ccnpletely solved is thet of develop-

ing an electrode pd: shich will give stable responee eai not be easily

deactivated in non-equeous nedie. Of the any conbinetions suggested

(6,2). the glusocelonel (sleeve type) electrode pair has given the

best results of the peirs tried in this investigeticn.

The preceding discussion is only s brief sketch of the developments

in non-aqueous titrinetry. For s more complete treeteent, Riddick'e

review (315,35) , Frite's booklet (6), end Pelit's monograph (29) ere

excellent sources for interaction on this topic.

Ligh Frequency Ion-queens Titrinetg

Jensen and Perl-colt (21) who developed the first practical high

frequency titretion epperetus in this country were else the first to

recogniutb potentiel usefulness of high frequency titriletry for

non-equeous systems ." II‘hey reported in their originel pepsr the success-

m1 titretion of hensoic ecid or 2-phthelio eoid dissolved in eoetone

dth eodiu lethoxide titrent .

""H

For the next few years the literature on high frequency oscillat-

ors was may devoted to improving instrumentation. Janhousld (20)

has an excellent review covering this period.

The first successful high frequency titratione in glacial acetic

acid with perchloric acid dissolved in glacial acetic acid were reported

by Wagner and Kaufman (37) . They compared potentiometric and high

frequency results for aniline, p-teluidine, pyridine, and Ly-bis

(2-cyanoetml)-2,s-dimthylpiporuine and expressed the view that

results obtained fron high frequency titrations for these bases compared

very fevombly with those obtained from potentiometric titrations.

Unsuccessful titrations were reported for urea, ponitroaniline , and

g-nitroaniline. ’

Jankovski (20) titrated successfully B—quinolinol, aniline, hexa-

sethylenedialine . pyridine , diethylsniline , and 23de in glacial

acetic acid with perchloric acid dissolved in glacial acetic acid.

lie satisfactery‘end point for urea was obtained.

Dean and Gain (3), using a Sargent 'Oscillcmeter,' reported good

results for the. titration of salicylic acid, potassium acid phthalate ,

bensoic scid , g-nitrcphencl, boric acid, and smonilm ion. The samples

were dissolved in dinethylfernmside and titrated with sodium methoxide

in benzene-uthsnol. . The end point for phenol was unsatisfactory.

Lippincott "and Timick (26) titrated a series of week, substituted

snilines in glacial acetic acid with perchloric acid dissolved in the

sane solvent, reporting results which compared very favorably with

data obtained by pctentiometric and classical conductinetric titrations.

rHi

Ill

It

|.F

Ii5

d.

‘Irl.

a»

The compounds successfully titrated were I

Aniline p-bronoeniline g-nitroaniline

penicillin p—aminoacetophenone p—nitrosnilino

p-toluidine raincbensoic acid

poohlcroeniline goutmenilim

They also ‘3‘! able to carry out differentisl titrstions , not possible

by potentialetrio or conductisstrie nethods, of some pairs of the sub-

stituted snilines listed. above .

Lane (25), in order to evaluate the usefulness for non-aqueous

titrilsetry of a portable instrument designed by Daedall, g _a_l_._.(h),

titratedse-euskbssesinglscialscetisseidendsenemkacids

in ethylenediesine. the cemennds were:

In Glacial Acetic laid“

Imidins ‘

Decemethylenebispyridiniun nitrate

Wronquineline

o-Phenanthroline

adrenaline

Phenasine

itreaniline’

dine

Homethylssetetrenine

2(2-Hydrcxypherwl) obensiminasole

Dianisyldilethylphosphoniull iodide

Dianisylethylnethylphosphoniun iodide

Dishisyllsthylphosphine

Tetraethylslncniun bromide

tetrsethylauoniun iodide

Tetreethylasncnilm nitrate

Tetralethylsmncnilnn iodide

Ethyltrinethylsmoniun iodide

Phenyltrimethylslmoniun iodide

Homethylenebispyridiniun nitrate

Tri (g-hydrosyphenyl) ~sulphoniun chloride

'i'he quaternary moniun halides were determined by the mercuric

acetate rougent nethod suggested by Pifer and wollish (31) .

In Etglenedismine

Dinedons

5-Hitrophencl

-Hydroxyquinolino

2 ( 2-Bydrcxypheny1) -bensoxasole

h-Hydron-l,2 ,3-bensselenadiasole

2,3-Dihydrexy-S-nethcmuinoxaline

S-Hydroxy-Z ,3-diphenquuinonline .

Srfiydroq-Q ,J-di (2-pm-1dy1) quinonline

S ,8-Dihydrcxy-2 ,3-tetrsmethylenoquincnlins

S ,Bquhydroxyozuphenquuinenline

S ,B-Dihydrclqv-2-isoprcpquuinoxfl.ine

5 ,8-Dihydrqu-2 ,J-pentanethylenequinesalins

Tri (rhydrozyphenyl)~phospine oxide

Iehidate and Hasui (38) titrated a series of nonobasie and dibasic

carbonlic acids in benseno-nethanol nixed solvent nith sodium nethexide

in beneene-nethanol. They reported the titration of a series of

alkaloids and acid“ salts of sons organic weak bases dissolved in water

or eater-alcohol with perehlorie acid in glacial acetic acid (39).

In another paper (to) the titration of amino acids and organic bases

dissolved in hormone-methanol eolvent containing some acetic acid with

perchloric acid in" glacial acetic acid was reported.

1“H

' - -

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v

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. .|

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I

a...“

i.

1’ ' ‘

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s.r

' Q

'Q

SLJ . I

.

A ‘ ‘i K . .

- . , - a

. v \

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e

.

e- s

I

y

s ‘ v- <

Reagnts

No attempt to repurify the organic acids used in this investi-

gation (except where noted below) was nude since most vere nominally

'pure." 1 cosxparison for a given compound of results obtained by

potentiometric , high frequency, and visual methods 13s deemed sufficient

basis for Judging the fluorite of high frequency titrinetry for ssak

acids. To check the purity of phenol by an independent nethod, the

brcnination procedure described by Siggia (36) as employed. Although

Biggie. states that resorcinol can be determined in the seas Inner,

satisfactory results sore unattainable.

The compounds titrated, source and labeled purity, are:

Weak icids'

idipic acid

obsueie acid

nzoic acid

Halcnic acid

Methyl salicylate

rNitrobensoic acid

B-Quinoliool

Resacetcphenone

Salicylic acid

2 ,h,6-Trichlnr0phsncl

Vanillin

Veg Weak Acids"

p-Bensylphenol

Sstechelhmol

Recrystallised from acetic acid

Eastman White Label

Primary reagent grade (General Chemical

Dow Camus 0m)

Eastman White Label

Eastman white Label

Eastnan White Ltbfll

Estman Yincite Label

or. (Coleman 5 Bell)

Unknown

0.3.9. (Retort Phanaceutical Co.)

Eastman White Label

Elm White Label

Recrystallised from toluene

‘Thh classification will be used throughout the thesis to designate

“compounds sinilsr to bensoic acid in their p]! values.

This classification will be used throughout the thesis to designate

compounds sisilar to phenol in their pK values.

TH!

Hydroquinone Eastman White Label

2-Hydroxydiphenvl Eastman White Label

-Ne.phthol Matheeon Company

henol Eastman White Label

Phloroglucinol Eastman White Label

Resorcinol Eastman White Label

p—l‘ert-anylphenol Eastman Yellow Label

Other chemicals used were:

mStandards: bemoio acid, potassium acid phthalats,

National Bureau of Standards or winery reagent grade.

Other Che-inlet potassium natal, sodiul natal, antiw

natal, lithiun chloride, potassiu- bro-ate, potassim

bro-ids, potassiu iodate, potassiul iodide, and

sodiu thioselfate , cheniedly pure.

Solvents: ' butylaaine, Bastian White Label; ethylenediuias,

Eustace, 95-40013 isopropyl alcohol, ethanol, methanol,

and bemene,~oheeically pure grade; diaethyltorsanids,

Hathesen's technical grads .

Technical grade dinethylfornanide required a blank correction of

approxilately 0.01; mini-equivalent per 150 milliliters . Dinethyl-

tcrlsanide distilled at atmospheric pressure through a six foot long

glass column packed with glass helices was found to have a larger blank

correction than the charge (0.05 milk-equivalent per 150 milliliters

solvent after distillation). Thus the dilethylforlanide used in this

investigation was used as purchased. The blank was determined by con-

paring the mount of titrant consumed with the theoretical alount of

titrsnt required for a know: weight of bensoic acid. Direct potentio-

eetric deternination of the blank was found to be unreliable. To prevent

additional absorption of atmospheric carbon dioxide by the slightly

.

t

\

2 1

\

O

a..-

10

basic dinethylfornanide,-the solvent was stored in glass bottles and

transferred to the titration cell by'neans of a 50 milliliter auto-atic

burst provided with guard tubes filled with ascarite'. “on med'

nitrogen was used to force the solvent from the reservoir into the

burst. The atopcock:of the buret_uas not greased since any grease

extracted by the dimethylforeanide obscured high frequency and points.

Alcoholic pom-aim hydroxiio“ (0.11: one 0.2611) use prepared by

dissolving, with gentle heating, sufficient potassius hydroxide in too

liters of isopropyl alcohol. After allowing the solution to stand for

twelve hours, it ens filtered through a coarse sintered glass filter

to remove the insoluble potassium carbonate. A nitrogen atlosphere was

provided during the filtering operation to exclude atlosphsric carbon

dioxide. The filtered alcoholic potassium hydroxide sas stored in glass

bottles and dispensed from calibrated autosatic'burets. The burete were

provided edth guard tubes filled.udth escarite. 'Oil pumped' nitrogen

use used to force the titrant free the reservoir into the berets.

These precautions vere taken to protect the titrant fro. at-ospheric

carbon dioxide. The alcoholic potassium hydroxide was standardized

against potassium acid phthalate dissolved in carbon dioxide-free dis-

tilled water, using phenolphthalein.ae the indicator. .A.feu'of the

standardisation titrations were carried out by high frequency titrinetry.

One tenth normal potassium nethoxide and 0.18 sodiul‘aethoxide

were prepared and standardised against benzoic acid as described‘by

Frits (6).

*rm to; alcoholic potassiun hydroxide is used in this thesis to

designate potassius hydroxide dissolved in isopropyl alcohol.

The non-aqueous indicators, thynol blue , ass violet, and 3-nitro-

aniline, sore prepared as suggested in Prue's-booklet (6).

Potassiu- beusats reunited for obtaining a high frequency re-

sponse curve for potassiu heneoate in dinethylfcreaeide as prepared

by adding potassius hydronds dissolved in otl'sanel to an alcoholic

solution of bensoic acid. The resulting precipitate as isolated by

,filtrstion, recrystallised from hot alcohol, and collected by filtra-

tion. The precipitate use then dried in a tacuus desiccator for 148

hours .

Apaatue

i Fisher 'Titrisetsr' vas used for all potentiometrie titration.

Various oc-binations of the electrodes listed below were used:

1) autism, 2) Doom #1196 class, 3) seem #1170 fiber type

sale-cl, and h) ink-an #167041 sleeve type calesel. ~

1 lssfase ledel ace 1!» Conductivity Bridge, in conjunction sith

a platinissd platinus i-srsion electrode pair («11 constant at 0.1),

see used for the. cenduotieetrio titration.

The capacitative type high frequency instrunent used in this

investigation see a duplicate of the prototype designed and built by

Johnson (22). The progress of a titration as followed by measuring

the oscillator tubs grid current changes dth a Hodel m Sargent

Polaromh.

By the use of various combinations of capacitative type cells and

coils or coaxial half-save line the operating frequency of the

instrument could be altered. Tee capacitative type cells were

e.ve

12

constructed. One was a band type in which two one-half inch side

copperheads, scented one above the other approximately one-half inch

apart, encircled the titration vessel. The other consisted of tee

brass plates, one-half inch wide by one inch long, nounted against the

titration cell at the sale level, but three quarters of an inch apart.

Other constructional details are identical with those presented by

Johnson (22).

Operating frequencies were nessured nith a Signal Corps let.

limiter-3042554 frequency ester.

Thefreeuencis‘s fervarieuseeebinstieneefesnsaedeeileer

half-save 11‘ '1'. I

‘.

Cell Inductance tremor;

Band type h2 turn coil 11 In

Bead type 8 turn coil 36 MC

Plats type b2 turn coil 15 no

Plats type 8 turn coil h9 no

- Plats up. Half-rm" line (as an.) no no

The auto-atio bursts were calibrated using the titrant to be dis-

pensed free then as the calibrating liquid. The coefficients of

cubical expansion of the titrants were domd in a 25 milliliter

dilate-ster at five degree intervals free 20 to 35°C. The coefficient

of cubical expansion for 0.1! potassius nethoxids in benzene-Isthanol

(lO/l) was found to be 0.12% per degree centigrade; for 0.1! alcoholic

potassiu hydroxide, 0.111 per degree csntigrade. will release of

titrant recorded in this investigation were corrected to 20°C.

1mquenoies were measured with the titration vessel filled with

150 sillilitsrs of diaethylforssnids.

13

ill analytical eeighiue sore weighed to the nearest 0.1 nilliuan,

enploying weights calibrated against nation). Bureau sf standards

calibrated Heights, Ltd. Tssthc. 87925.

Titration Procedures

33221..

The compounds listed on page 8 as weak acids vere dissolved in

so nilliliters of dinethylfornanids and titrated eith 0.1: sodiu-

nsthozids to the first blue color of sec violet indicator (6). Before

adding the eanpls the acid inpnrities in the dinethylfcrsanide were

neutraliscd uith titrant to the sane blue color.

The compounds listed on pages 8 and 9 an very weak acids ears

titrated in 50 milliliters of ethylenedianins to the orange-red color

of rem-uninh- with 0.1: sodiun nethoxide (6). u in ths case of

dinethylferesnide the acid inpuritiss were neutralised before the

addition of the sanplefi

Pmticnetrie

three electrode ccnbinations were used in this inveetigationc

l) anthem-glass syste- for titrations of henscic acid dieeclved in

dinetlvlfornanids with potassiun nethoxide, 2) calonel‘. (fiber)-¢lass

systel for titrations of weak acids dissolved in dimethylfornanide with

alcoholic potassim hydroxide, and 3) calonel (shard-glass cysts. for

titrations of very weak acids dissolved in dinstlwlfornanide with

alcoholic potaseima hydroxide . -

The Fisher "l'itrinster' was balanced at 0.5 volts.

1h

The eanplss vere dissolved in 75 milliliters of. dinsthylfereanide.

A nitrogen atmosphere. was provided to protect the titration solution

from atnoepheric carbon dioxide. Increments of 0.25 eilliliter of

titrant sore added at the beginning of the titration. Near the end

point the increments were reduced to 0.1 nilliliter.

Conductinstrio '

The Serfass Conductivity Bridge was operated at 60 cycles.

External capacitance cespsnsation use not seploysd since it did not

seen to inprevs instrueent balance. .

The saeple of benseic acid use dissolved in 100 nillilitsrs of

diuthyiten-ude. The nuance vessel use rovidsd sith a sever to

exclude ethosphsrie carbon dioxide.

m Preguenox

The inetrunent was allowed to m up for a sinieu «two here

in order to stabilise its response.

The sample see uighed to the neareet 0.1 eilligrae and transferred

to the polyethylem tit'ation vessel. Tide vessel was then placed in

the cell assesbly and a polyethylene cover, containia opsums for a

nitrogen gas inlet,' glass etirrsr, and beret tip, was slipped over the

nouth ef the titration vessel. The ector driven glass stirrer h“

positiued so that'ths paddle blades ssrs below the bade or plates.

oh- hmdred and fifty amine». sf selvent eas transferred to

the titration vessel with a 50 milliliter actuatic burst. After the

nitrogen flow had been adjusted to a noderate rate and the opening

for the burst tip plugged with a shall cork, the solution as stirred

15

for approximately 15 ninutee to establish temperature equilibrimn in

the solution.

thus the solution was attaining temperature equilibriun, the

3argent Hodel III Polarogrsph see tmed on, the span voltage set at

one volt, and the proper sensitivity (usually 0.100 nioroanpere per

this.) selected.

After the required uniting period the titrant burst was positioned

with its tip below the surface of the solution in the titration vessel.

Unless a cceplste titration curve was desired, the bridge cent-cl

of the polarcgraph me not adjusted to bring the scale pointer to the

lower end of the scale until approxinetely all but five nilliliters of

the theoretical mount of titrant required had been added. This step I

was taken because the initial formation of the salt of any of the

coepcunds titrated so “loaded" the instrument that either an extrenely

large compensation setting was required to bring the pointer onto the

scale again or the instrunent went out of oscillation for the particular

bridge control setting.

Once the initial amount of titrant had been added and the final

adjustments of the bridge control mode , the titrant was added in

increments of 0.25 or 0.50 nilliliter. Recorder readings were taken

30 seconds after each addition of titrant. Timed readings were

necessary because of recorder fluctuations. Usually, readings were

lads over a span of 10 milliliters, five milliliters before and five

nilliliters after the-end point.

16

DISCUSSION OF RESULTS

Respgnse Curves

Response curves are obtained by adding in known increments to

pure solvent one of the substances removed, added or formed during an

actual titration and recording the oscillator tube grid current changes

produced. Semi-log paper is used to graph response against nolarity

because the concentration ranges involved in determining response

curves extend through several powers of ten. There is no logarithmic

relationship between response and molarity.

If response curves for the titrant, titrant diluent, the compound

being titrated, and the salt formed during the titration were available

for a given frequency, theoretical titration curves for a given solvent

could possibly be constructed. Usually only the response curve for

the addition of titrant to the solvent is obtained.

The response curves vary from hell to '8' shape, depending on the

frequency, solvent, and titrant selected. Figure 1 shove the effect

ef’frequency'ohangee upon the shape of the response curves. The linear

portions of the response curves indicate the optimum concentration

level at ehich the response of the instrument is linear and large for

changes in concentration. This information is used to select the proper

unpl- size to obtain optimum linearity in the titration curve .

i rather couplets survey'at 11.negacycles of the response curves

for the various elements involved in the titration of bensoio acid

in dilethylfonanide with potassium nethoxide was made because of the

l7

poorly defined end points obtained for this compound. From curve 0

of Figure 2 it is apparent that the response change due to the dis-

appearance of bemoic acid during the course of the titration is “all.

The slopes of the potassium bensoate curve (curve A, Figure l) and of

the potassium nethoxide curve (curve E, Figure l) are similar. Little

or no change of slope of the titration curve can be expected when ‘

potassiul bensoate ceases to be formed and the first excess of potassiu

nethoxide is added. Benzene, methanol, or a eixture of the tee caused

no response change when added to dinethylfornanide.

The response curve for alcoholic potassium hydroxide was detersined

at lhl negacycles. (Figure 3).

Titrations in Bem'eneiiethanol Solvent

Woman Hethoside asW

h no

A ratio of one part benzene to one part methanol was found to be

a satisfactory lined solvent for the titration of p-aninobensoic ,

bensoic , nalonic , g—nitrobensoic , or salicylic acids 14th potassium

lethozide titrant. Smooth titration plots and distinct and point

breaks are obtained for these weak acids, as shown in Figures 1: and 5.

The titration results for these compounds are listed in Table II.

lle end point breaks were obtained for the titrations of resorcinol,

hydroquinone , catechcl, or phenol. The acidity of methanol precluded

the successful titration of these compounds in this solvent system.

Pare bensene see also tried as a solvent for phenol but the instrument

she'd no response on adding titrant to this solvent, even when 0.2 grail

of lithiun chloride was added to provide some instrument loading.

SBBiEWIiNBO

SOLVENTZDMF

FREQUENCY

A;ISMC

.4

BI4IMC

C)49MC

"1”

ll

eI

1

Doom

0.00l

0.0!

0.I

LO

MOLESPER

LITER

FIGURE

I."RESPONSECURVESFORKOME,AT

VARIOUS

FREQUENCIES

O

‘NOIiOB'HBO 3'! V OS

1..)

CO

A)K000c

B)KOME

--

0)

I'D-000¢

400M

_-L

SOLVENT?DMF

FREQUENCYI

llMC

L

SHBiBWIiNBO ‘NOIiOB'IJBO BWVOS

Il

lI

00000:

0.000:

0.00:

0.0|

MOLESPER

LITER

FIGURE

2.

RESPONSECURVE

19

20CM

ssaiawuua 0 ‘NOIiOB'IJSCI awos

‘i

SOLVENT:OMF

FREQUENCY:

I41MO

Il

I

0.000|

FIGURE

3.

0.00:E

0.0:

0.:

HOLES

PERLITER

RESPONSECURVE

FOR

ALO.KOH

L0

20

rI

1I

I:

I._

gTHEOR.

E.

P.

’.

A)

BENZOIOACID

5.2:ML

ee)

SALIOYLICACID

:0.79ML

'IIMC

‘7

'—

'B

IO.72ML

'—

lI

MLI

lJ

lI

ll

Jl

"

MILLILM’ERS

FIGURE

4.

H.F.TITRATION

CURVES

FORWEAK

ACIDS

INBENZENE—

METHANOL,KOME

TITRANT.

suaiawuusc mouse-1330 awos

21'

‘iNVHiIi3WOX‘1ONVH13W

-3N32N38

NISCIIOVMVBM

30;:

saAsn'o

NOIiVHiIJ.'d'H'QBHnald

a,seam-Inn»:

.e

‘e

I'L

'Tl

lI

T

0"IN!

'

O

‘.

.0

.1w

ce'e:

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..

..

..

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0-.._

’.\I1w

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..

W0”

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.0

0O

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aO

Q.

.__'_I

h—

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C_

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::.

17;!

Iclovomznssomwv-d

(0

.

T-e'cl

0:0vclczuascsim-u

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0:~0‘:v:~

(v

3'31:03:41

”

Il

Il

Jl

Jl

O

O

O

ssaiawunao ‘NOIiOB'UBO Envos

23

Titration in Dingomlforlaslide Solvent

Potass m: si e as itrant7

Conductieetric

The titration of bensoio acid with potassium eethoside was the

only conductinetrio titration perforeed in this investigation. The

oondutinetric titration curve is very similar to that obtained by

highfrequency titrinetry for the use compound as is shown in Figure 6.

remunetrig

An antiwar-glass electrode pair was used in conjunction with the

standardisation of potassium nethoxide with bemoio acid .‘ no other

compounds m. titrated potentinetrically with potassiue esthoxide .

53h Pmnengz

Ml could not be titrated successfully with potassium nethoxide

because the acidity of the methanol present in the titrant solution

lashed the end point.

Either poorly defined or no end point breaks were obtained for

the titration of busoic acid, catechol, or nethyl salioylate.

Guidance of cateohol in the presence of moss titrant may have pro-

tested its successful titration (21:).

Vanillin, 2 ,h,6-trichlorophenol, resacetophenone , or 8-quinolinol

sore titrated satisfactorily. Typical titration curves for these

' eupeunds are show in Figure 7. Results are listed in Table II.

2h

,CENTIMETERS

SCALE

DEFECTION

F:

e ' -

200M 2

A . 5.60 ML .

/ l5 MC e —‘

0.

e e

e . 8

0 . ~P— Z

. 5 H Uo 4" Io’ OHM' c

o

I O. .h..__ g

A z

. orn

O * B) CONDUCTIMETIC 3J3ML_

B — . — 3J0 ML

./

0 SOLVENTIDMFe TITRANT: KOME

.° THEOR

A) HIGH FREQUENCY 554 ML

IML

III 1' 7 L

MILLILITERS

FIGURES. H. F. AND CDNDUCTIMETIC TITRATION

CURVES FOR BENZOIO ACID.

25

T l I l l '

_.- THEO'. .P

A) 8-QUINOLINOL 13. L

B) 2,4,6-TRICHLORDPHENDL l5. 0 ML

m- CHESACETOPHENONE .. “.78 ML.1

:3 D) VANILLIN l4.76 ML

+- II MO I-

m___

2 _ ‘; 40M ”3.72 ML

2 v

3"“ ' ' *z. w

o - ' B

m ’ “L73 ML.1 e

ur- .. ,' ' g ' ‘ -w I ' .

o

mJ

<

o

m

MILLILITERS

FIGURE 7. H.F.TITRATION cuaves FOR WEAK ACIDS

1NDMF, KOME TITRANT.

26

Titration in Dimeth ltormaxnide Solvent

WW”

Potentiometric

During the ”culinary investigation of alcoholic potassium

hydroxide as a titrent for weak and very weak acids a sleeve type colonel

electrode was not available, so a fiber tip type was tried. The fiber

tip type calonel electrode was usable with the weak acid class even

though it was less stable than the sleeve type. A serious draw-back to

’ the utilisation of the fiber tip type oalcmel electrode in dinethyl-

rename; is the deposition of potassium salts on the fiber tip (2) .

It was observed that the electrode became sensitive to body capacitance

upon prolonged use. To mitigate this effect somewhat, the electrode was

soaked in inter for a short period after a series of seven or eight

titrations. i very erratic titration cm was obtained for phenol,

Figure 6, curve B, when a fiber tip calms]. electrode was used. The V I

titration curve for 2,14,6-trichlor0phenol, Figure 9, curve A, shows a

large drop in potential imediately after the end point inflection.

The calmel (sleeve typc)-glass electrode system proved to be

responsive and stable for titrations of nest of the very weak acids.

Curve 3 of Pig” 9 and curve A of Figure 8 are typical for these

compounds. The end point inflections were small but sharp , emept in

the case of 3¢hydrozydipheny1. For this compound almost a milliliter

of titrant use required before the potential leveled off. after the

initial sharp rise at the inflection point. A representative titration

curve for this’conpound is curve C, Figure 9.

Si'IOAI'I‘IIW

ii—fi-

L

I'

Il

lT

l

PHENOL

INDMF

TITRATE

WITH

ALO.KOH

CURVE

OALOMELTYPE

ASLEEVE

BFIBER

TIP

-w

I

JJ

ll

FIGURE

8.

MILLILITERS

CALOMEL

ELECTRODE

PERFORMANCE

27

II

II

.I

II

l.

LTHEOR.

E.P.

'A)2,4,6-TRICHLOROPHENOL

23.9IML

..

.

B)"P-BENZYLPHENOL

4.53M

~

0)o-HYDROXYDIPHENYL

4.36M

.

R I I

A53.0.

3

_.23.91ML--

4'55ML”

sue/\I'I'IIN

L__L

JJ—

L1

1‘,

L

MILLILITERS

FIGURE

9.POTENTIOMETR-ICTITRATIONwaves

FORVARIOUS

PHENOLSINDMFTITRATEDWITH

ALG.

KOH-

29

Titration results for the very weak acids are listed in Table 1.

mm... results fer the weak acids are listed in Table II.

High Pregnancy

Distinct end point breaks were obtained for titrations of phenol,

rbenzylphenol , p—brc-ophonol , g—hydroxydiphenyl, or i-naphthol, all

very weak acids. Figures 10 and 11 are representative of the type of

titration curves obtained for these compounds. Titration results are

listed in Table I.

Para-tert—anylphenol failed to yield stoichimctric results even

though the end point breaks were sharp and well defined as shown by

me C in Figure 10..

Stoichionetric results were unattainable for catechol or phlcro-

glucinol . Black discoloration of the solutions after titration indicated

oxidation of the compounds in an excess of titrant. No attempt was

made to titrate resorcinol or hydroquinone . A possible solution to

this oxidation problm muld be to bubble nitrOgen through the solvent

to remove any dissolved oxygen before adding the sample.

The titration curves for benzoic or salicylic acids were un-

_ satisfactory. it best, the scattering of individual points blade the

selection of the end point difficult.

Titration plots, Figures 12, 13.and 114, for adipic acid, B-quinoliml,

pcanimbenzoic acid, methyl salicylate , malonic acid, resacetophenone ,

g-nitrobcnsoio acid, 2,h,6-trichlor0phsnol, or vanfllin ranged from fair

to good. Titration results are listed in Table II.

4CM

s

.c

..THEOR.E.F."'

'A)o-HYDROXYDIPHENYL

no.5:ML

..

'B)P-TERT-AMYLPHENOL

IO.|OML

ee

C)P-BENZYLPHENOL

9.32ML

,.0

MIMC

’L

IMI.

I

Ij

«.1

iL

1I

||

|.5

MILLILITERS

FIGURE

IO.H.F.TITRATIONCURVES

FORVERYWEAKACIDS

INDMF,

ALC.KOH

TITRANT.

—

_l

2

w

m

of

C

C

4

SHBiBW llANB o ‘No uoau 30 awos

4CM

se

O

B,

lno.9:ML

0

.c

,”.2546ML

0,

’:4.MC

T'HEOR.E.P.

__

..

'AIM-BROMOPHENOL

no:ML

.°

3)e-NAPHTHOL

”.04ML

.,_LM_L_'

c)PHENOL

25.72ML

"I

Jr

1l

14

lI

MILLILITERS

FIGURE

ll.

H.F.TITRATIONCURVES

FORVERYWEAK

ACIDS

IN

DMF,ALC.KOH

TITRANT.

—-I

.1

O

SHBLSWILNBO ‘Nouoauao awos

7';31

A)H-NITROBENZOICACID

3153;155'

.’

_.e)P-AMINOBENZOICACID

14.47ML.

0_

C)ADIPIC

ACID

'6'96o

s

I4IMG

se

Ie

.

I105M

sIe

AO

'O

.II¢57M.

”T

4CM

''

."6.66ML

W"—

Il

l'

Jl

MILLILITERS

FIGURE

l2.

H.F.TITRATION

CURVES

FOR

WEAK

ACIDS

INDMF,

ALC.KOH

TITRANT.

.

.

suaiawuuao L‘NOIlOB'Id‘BCI 31'vos

ll._

.

-b—‘

32

SHELBWILNBO

‘NOIiOB‘IdBO Envos

A)B-QUINOLINOL

I3.I6ML

a)METHYL

SALICYLATE

[4.02ML

__p)

MALONIO

ACID

2272ML

.

40M

.e

'MIMIC.

''

THEOREIR

'0

—~

C

o.

”2.98ML

s

e.

-

s'

II334ML

22.I5ML

~l

Il‘

FIGURE

MILLILIT

RS

I3.

I-I.F.TITRATIONCURVES

FORWEAKACIDS

IN

DMF,

ALC.KOH

TITRANT.

\l)

b.)

4‘CM

Ce.

ee

.e

CI

Q.

4.5.55”.I

0I293ML

.s

I

IO

eI

“/°

0B

ey

.2249ML

C

'.

''4'”'0

«rmeoeae

sA)VANILLIN

ZZJSML

'—

0IO)2,4,?-TRICIHLOROIPHENOIL

5#7ML

MILLILITERS

FIGURE

I4.H.F.T|TRATIONCURVES

FORWEAK

ACIDS

INDMF,

ALC.KOH

TITRANT.

O

J _ -

suaiawuuao ‘Nouoa‘uao ewes

3b

35

As might be expected from pK values, the end point breaks for

adipic or salonic acids were very well defined. The titration plots

for EganinObsnzoic or genitrobenzoic acids, which have pK's similar to

adipic and nalonic acids, did not exhibit sharply defined end points.

There was such scattering of individual points of the plots for these

acids. The whole weak acid group, except for adipic and nalonic acids,

showed this tendency for scattered individual points of the titration

plot, but not to such a marked degree.

Differential titrations of mixtures of phenol and 2,I4,6-trichloro-

phenol were attempted.‘ The data mm the two titrations performed,

although not conclusive, indicate the feasibility of the simultaneous

titration of‘ teak acids of different pK values by high frequency

titrinetry. The results are:

final Run IIw

Tam widCCCCC.CCCCCCCCCCCICCCCCCCC 100.6% 9602‘;

2,h,6-Trichlor0phenol............... 97.9 112.8

Pmn°1CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC 103.2 82.3

Figure 15 shows the titration curve for Run I.

Titrations in Dimeth lfornamide Solvent

(So-dim Hothoage as Titrant)

Visual

Only two weak acids did not give entirely satisfactory titrations

With aso violet indicator. The end point for adipic acid was obscured

by precipitation of its potassium salt. Fading of the end point was

observed then nalonic acid was titrated. Titration results are listed

in Table II.

I I I I F

__e ,

. O

. O

s ’ .

e "T . ' “U 4 OM

. . .

I-C

uI__L ' . _

z /0

F5 0 '

Z ”.48 ML _ C... e _

‘3" ~ - .A ,/ .

z.

2— - s -..—

O . /.

In e ’

..I ___ 5.53 ML __

LI. 0

‘3 e B O

m_e , THEOREE

.4 , . A) TOTAL ACID II.42 ML

3 B)2,4,6 TRIOHLOROPHENOL

‘9 . e5.65 ML

*- SOLVENT30MF"‘

e TWRANTiALcoKOI-I

. I4I MC F| L

L If I I I _ ~’ L.

MILLILITERS

FIGURE l5. H.F. TITRATION FOR A MIXTURE OF

PHENOL AND 2,4,6—TRICHLOROPHENOL.

37

Titrations in Eth lenedienine Solvent

' {Sodiu- Ethofide as Titan”

1.121..

The color change fro: yellow to orange-red for g—nitrcaniline

indicator used for titrations in ethylenedianine with sodiue nethoxide

is not as distinct as the change to blue of ass violet in Iii-ethyl-

fornaeide. Little difficulty use encountered in determining the end

point. Titration results for the very weak acids are listed in Table I.

Tabulation of Titration Results

The compounds titrated in this investigation were divided into

tee groups, weak acids and very real: acids. This division is based

upon relative strengths. The tables of experinental results vere there-

fore organised on this basis.

The titration results obtained free high frequency, potentiometric ,

and visual procedures for individual eoepounde are grouped together

under the none of the ccupound in order to facilitate chparison.

The sin of the circles used in the titration plots is not pro-

portional to error because of uncertainty as to the sagnitude of error

introduced by fluctuations of the recorder.

1!ng

I.

38

Matinee-mo

iewe ea cc

nag §§ an“mn.nu en

sag an §§

w“

uA

A.

’Mn‘mm;W9:

em.

or).

609170

omen

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Unsatisfactog SolventiSystsns for Hg}: Frequenq Titrimetg

Titration of phenol in butylanine with potassium nethoxide was

attempted, but the instrument would not respond to addition of titrant.

The sane phenomenon occurred when titration of bensoic acid or phenol

were attempted in benzene with potassiun nethoxide. Even the addition

of lithiun chloride had no effect. Benzene-iscpropyl alcohol (9/1 or

1/1) nixed solvent likewise gave no instrument response when the

titration of phenol with alcoholic potassiun hydroxide was attenptod.

M

WAND CONCLUSION

without knowledge of the acorn-soy of the comparison nethods it

is inponible to appraise the accuracy of high frequency titrinetry

for weak and very weak acids. This study one intended as a survey to

detersine mother such acids could be titrated by the high frequency

nethod, therefore, no special effort was put forth to study factors

Ihich affect the precision of the nethod. 1‘s provide some basis for

V superfine, lean values for the respective nethods have been ecnputsd

and these values tabulated below. Only those values agreeing tithin

twe per cent were included in computing new values .

Although only relatively few high frequency titratione Vere per-

forsed in beneeneunethanol, this solvent systen, in conjunction Iith

potassiul nethoxide titrant, scene to offer nsny‘ advantages for high

frequency titrinetry of use]: acids. These advantages are smoothness

of titration plots , sharpness of the end point breaks, availability

and relatively low cost of the solvents, lack of blank correction, and

lack of objectionable odor. Successful titration of very weak acids

is not possible because the end point is leaked by the acidity of the

nethanol present.

successful high frequency titratione of p-eninobeneoic, bsnseic,

nelsaie, raitrobeneeic, and salicylic aside were performed in bensene.

nethansl fixed solvent ulth potassiun nethoxide. The end point breaks

for hensoio acid were sharp and tell defined , but no coeparison can

he nede 1th results obtained by potentioIetric or um nethode since

he

the titrant has standardised against benscic acid employing these

uthode. The titration results for the others—area

.. High 9mm; Potentialstrig Vista;

hinobeneoio asid . - 99.2: 101.11: 100.9:

01110 99.6 erratic 100.14

n-litrobensoie acid 100.3 99.8 99.1%

§alicylio tom 99.9 99.0 100 .1

he successful high frequency titratione. of phenol, catechol,

lvdroquinone, or resoroinol were accosplished employing this solvent-

titrant syetu.

Only a few onennds were titrated in dissthylfornaside with

potassius nethoxids since alcoholic potassiue hydroxide proved to be a

far superior titrant for very nah aside. Bespousds which were success-

fully titrated by the high frequency nethod were B-qeinelinel, reesssto-

phenone, 2,h,6-trichlmphnol, and vanillis. the titration plots were

ssseth with um. or no scattering ef individual pointe . the titration

results arse

mg Frequencyfll’otentioletric M.

B-Quiselinsl 99.81 101.35 101.1%

Resacstophsnone 99.9 99.9 --

2,h,6-friohlsrophencl 98.2 90.0 90.;

lo Visual titration! of resacetophenone were perfor-ed because of

insufficient couple. The end point breaks for bensoic acid, salicylic

acid , or nethyl salicylats ranged fro. poorly defined to indeterminate.

The acidity of the sethanol present in the titrant solution mined the

end point break for phenol or catechol.

“TEncept for salicylic acid these high frequency titration values

represent only one titration .

1“Only one high frequency titration was performed for each of the

compounds listed in the table.

-

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it

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I. _

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a

I.

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y-

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O

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a

-«o ~9- oo “or—n-

149

High frequency titrations of very weak acids in 'dilethylforneside

with alcoholic potassiun hydroxide titrant proved successful for the

'nonchydrc’sy phenols, rbenzylphencl , Bohracophsnol , g-hydroxydiphenyl,

L—naphthol, and phenol. Bone scattering of individual points of tin

titration plots was observed but this phencnenon did not interfere with

selection of the end point. The titration results are:

High bequency Potentionetrio Visa);

goBenaylphsnol 99.7% 100.55 ' 99.7%

p-Bronophenol 99.7 101.5 100.6

o-Hydrcxydiphenyl , 100 .7 101.11 100 .0

oNaphthol 99.3 x 100.6 100.11

m1* 1 - . 98.6 100.1 99.9

A result of 99.1 per cent as obtained for phenol by the standard

brednation nethcd. The end point breaks for potsrt-anylphenol were

sharp but the results were very erratic. High frequency titration of

catsohol or phlorogluoinol were unsuccessful, possibly because of

saidation in excess basic titrant. The titration solutions were that

after the titrations.

High frequency titrations of adipic acid, z-uiscbeuoie, bensoic

acid, nalonic acid, asthyl salicylate, ynitncbensoie acid, B-quinolinol,

resaoetophenene, 2,14,6-trichlcrophensl, er vanillin {m pox-toned

suscessfully in dilethylforsenide nth alcoholic potassium hydroxide

titrant. The titration results area

“The value listed under 'High Frequency“ results is the seas of nine

. titration values obtained from three series of titrations. Two

other values were discarded because of a large deviation free the

scan. Another series of titrationc, 102 .11, 911.11% and 102.11%, also

was clitted.

50

Eh Pregnancy Pctanticnotric Visual

Adipic acid 98.8% 98.53 100.5}

ininobenzoio acid 100 .5 101 .1: 100 .9

ado acid 97 .14 erratic 100.13

Methyl salicylate 98.6 98 .9 99.11

nofiitrobcnzoic acid 100.2 99 .8 99 .14

8-quinolinol 98.5 101.3 101.1

Resacetophcncne 100.5 99 .9

2 ,14 ,6-‘Iirichlorophonol 98 .7 98 .0 98 .5

Salicylic acid 101 .2 99 .0 100 .7

Ho visual titrations of resacetophcncne were performed because of

insufficient sample. Since bemoic acid was used as the standard or

for detemining the blank for the potentialetric or visual nethods ,

no comparison was lads. High titration results by the visual method

for adipic acid nay be due to the obscuring of the end point by the

precipitation or potassium adipate during the titration. The indi-

vidual points or the tum-.101: plots for m the m acids, except

adipic and nalonic, showed some scattering. The scattering ms largest

for bensoic and salicylic acids. This scattering lads selection of the

end point “that difficult.

High frequency titriletryi'or weak and very seek acids proved to

be reasonably accurate . Of the three eolvent-titrant systole used,

benzene-lethanolupotassiul nethoxide , dinethylfornanide-potassiun

nethende , and dinethylforaanid'e-elcoholic potassium hydroxide, the

last naned mm yielded the lost erratic titration p10“. The

scattering of individualpoints of titration plots and small change of

slope at the end point gave rise to difficulties in selecting the end

point for some leak acids. This solvent-titrant systen, homver, was

the only one eith inchieuccesstul titrations of very weak acids could

51

be performed. Rowena-methanol mined solvent appears to be the. better

solvent for the titration of bensoic, salicylic , and other teak acids.

there is little or no scattering at individual points or the titration

plots and the and point breaks are distinct.

Although comparable titration results were obtaimd for the...

dimetmrlfornanide solvent systeue by high frequency and potentiometric

nethcds, the high frequency nethod is more attractive sinee the

electrodes do not cone into contact on. the solution being titrated.

By the high frequency nethod very weak acids were titrated in dinethyl-

fornanids. Such titrations have not been carried out successfully by

an indicator lethod. ‘

A possible solution to the problem of end point detection due to

point scattering when the dinethylfomanide-alcoholic potassdun ‘

hydroxide system is employed would be to utilise an automatic recorder

in conjunction with a constant delivery burst. Mther titration

curves would possibly be obtained.

Since any inherent instability of the electronic and mechanical

systems of the Sargent Model III Polarograph is incorporated into the

reopen» values of the high frequency instrument, the substitution of

a potentiometer type 'nulling' arrangement «uploying calibrated

'helipct,‘ for the pelarograph might improve the stability of the

response of the inetment.

The titrations ears. almost exclusively carried out at lhl nega-

cycles . Possibly operation at a lower frequency would yield smoother

titration plots for some of the systems studied .

There me some difficulty dcfinhxg the end point because of .a

slight curvatm'e of the branches of the titration plots for some of

the compounds and a lack of a large change of slope at the end point.

Most of the titrationc performed in this investigation were dom with

0.1 H titrant, approximtely 10 times the concentration of the sample

eolution. Increasing the titrent concentration to 0.231 light produce

more linear plots and lm'ger change of slope at the end point.

53

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Dance-293

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