970 COHEN AND HODSMAN: OXIDATION OF THE NITRO- A N D

XCI I.-The I?I,Jluence of Substitution in the NUC~HLS o n the R a t e o f Oxidution of the SicEe-CJ&a. 111. Om*dation o f the Nit yo- aizd CIL1ol.onitro-deriuati.ztes of Toluene. By JULIUS BEREND COHEN and HENRY JAMES HODSMAN.

I N two foriner communications by Cohen and Miller (Trans., 1904, 85, 174 and 1622), the influence of the halogens in determining the rate of oxidation of the side-chain was studied. The present paper contains

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CHLORO-DERIVATIVES OF TOLUENE. 97 1

an account of the oxidation of the nit.ro- and chloronitro-toluenes. The same method has been employed as that previously described

The following table contains the result of five series of experiments in which the isomeric compounds are arrartged in the order of the quantity of acid formed, beginning v i th the least oxidisecl compound. For comparison the isomeric chlorobromotoluenes are added in the last column. The experimental details are given later.

(ZOC. cit .) .

Series I. 2 hours

a t 130-140". NO, : c1.

2 : 3 2 : 5 2 : 6 3 : 6 3 : 5 3 : 2 4 : 2

3 : 4 *4 : 3

Series 11. 24 hours

a t 130- 144". NO, : c1.

2 : 3 2 : 5 2 : 6 3 : 5 3 : 6

4 : 2 4 : 3 3 : 4

*3 : 2

Series 111. 44 hours

a t 123-133". NO2 : c1.

2 : 3 2 : 5

+2 : 6 3 : 5 3 : 6 3 : 2 4 : 3 4 : 2 3 : 4

Series IV. Series V. 4 hours 5 hours

a t 121-133". a t 119-122". NO, : C1. NO, : C1.

- 2 : 3 - 2 : 5 - 2 : G - *3 : 5

*3 : 6 - 3 : 2 - 4 : 2 - 4 : 3 -

-_ -

14 hours a t 139-147".

C1 : Br. 3 : 5 2 : 5 2 : 6 5 : 2 2 : 3 3 : 2

4 : 2 and 2 : 4 4 : 3 3 : 4

* Position of 4-chloro-2-iiitrotolnene.

Excluding the 4-chloro-2-nitrotoluene, which occupies nn exceptional position in the series and is considered Inter, the general result may be eumrnarised as follows. The compounds with the nitro-group in the ortho-position are least oxidised, those with the nitro-group in the para-popition aro most oxidised, whilst the metn-compounds stand midway between the two. It follows therefore tha t the rate of oxidation is mainly dependent on the position of the nitro-group. This is confirmed by the result of oxidising the three nitrotoluenes, from which i t will be seen tha t the same order is maintained.

* SERIES VI.-Oxidation of the Nitrotoluenes.

Time, 9 hour. Temperature, 128-131'. +Weight of

Weight Calculated as unchanged of acid. nitrotolnene. Found. Correct. substance. Total.

Ortho ..... 0.176 0.144 Very impire 147" 0.833 0.977

Pal R .. . . . . . . . 0 *30'2 0'248 234-236 238 0.769 1.017

* I n all series, t h e weight of each isonieride oxidiscd was 1 gram. t The weight of unchanged suhstance was estimated merely as a check on the

quantity of acid formed, hut, owing to the volatility of the chloronitrotolnene, the values obtained caniiot be regarded as very accnmte.

RI. p. of acid

Meta ...... 0.275 0.225 135-139" 140-141 0.760 0.985

On comparing the series of chloronitrotolnenes with the dihalogen derivatives i t will be seen that they both agree as regards the para-

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972 COHEN AND HODSMAN: OXTDATION OF THE NITRO- A N D

substituted compounds (4 : 2, 2 : 4, 4 : 3, nnd 3 : 4), a11 of which are more easily oxidised than the other meinhers of the series. It appears then that the rate of oxidation is to n great extent inde- pendent of the nature of the para-group present. I n the case of the ortho- and meta-substituents, the meta-halogen in the clihalogen derivatives retards the oxidation the most, whereas in the nitro- halogen series it is the ortho-nitro-group which possesses this function. The result is that in the dihalogen compounds the dimeta-compound occupies the first place and is followed by a series of ortho-compounds, whereas in the nitro-halogen series tho ortho-nitro-compounds stand first on the list and are followed by the meta-nitro-derivatives.

The position occupiecl hy the 4-chloro-2-nitrotolueno fluctuates in a way which we found a t first some difficulty in explaining. On examining the table on p. 971, it will be seen that the quantity oxidised appears t o vary inversely with the length of time during which the substance is in contact with the oxidising agent. Now, if the acid first formed is rapidly attacked by the oxidising agent, continued action m.ty result in i ts complete disintegration, accorn- panietl by the elimination of chlorine as hydrochloric acid. If this is the case both the amount of acid formed and the total quantity of the products would show a low result. The following experiments were undertaken in order to elucidate these points. The estimation of free hydrochloric acid in the oxidised procliicts was effected as follows.

The organic portion was extracted with ether from the contents of the tube and the aqueous layer drawn off, The ethereal layer w a s then washed with a little distilled water which was added t o tho aqueous portion already separated. An excess of N/10 silver nitrate was added, and, after filtering off Ihe silver chloride, the excess was estimated with N/10 ammonium thiocyannte.

In the following table the effect of protracted oxidation on the nucleus of the 4-chloro-2-nitrotoluene is well marked. The amount

SERIES IV.-Oxidation of the CIdoronitvotoluenes.

Time, 4 hours. Temperature, 121-133'.

CnlcnlRtcd of iin- +un- acid calcn-

of' chloi~oni tro- -7 suh- sub- cliloronitro-

Hydro- Weight Changed chloric

Weight as M. p. of wid. changed changed lated as

NO, : C1. acid. toluene. Fonncl. Correct. stance. stance. toluene. Total. 2 : 4 0'689 0.557 125-13s" 140-143" 0.309 0.896 0.165 1.061*

3 : 2 0%9l 0.6SS 175-150 179 0.326 0.914 0.009 0'923 3 : G 0-643 0.547 160-160 l(i5 0'405 0.952 0.003 0.955

* The excess over I grain of original substanco inust be placed to the account of

4 : 2 0.702 0.597 135-142 142-144 0'325 0.925 0.005 0.930

4 : 3 0'704 0.599 135-140 185-186 0.307 0'906 0.011 0.917

unchanged substance which cannot be accurately estimated.

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CHLORO-DERIVATIVES O F TOLUENE. 973

of hydrochloric acid set free is at least fifteen times greater than that derived from the other compounds of the series in which the nitro- group is not in the ortho-position.

This effect on the 4-chloro-2-nitrotoluene is shared by all the ortho-nitro-derivatives, for although they are less readily oxidised than the 4-chloro-2-nitro-compound, they all form hydrochloric acid and give a lorn total yield of products, The other isomerides not containing an ortho-nitro-group yield only comparatively small quanti- ties of hydrochloric acid. The low yields from the ort.ho-nitro-com- pounds are shown in the following series (111).

SERIES 111.-Oxidation oJ the C'hloi.oniti.otoluenes.

Time, 4& hours. Temperature, 123-133'.

NO, : C1. 2 : 4 2 : 6 2 : 3 2 : 5 3 : 2 4 : 3 a : 5 4 : 2 3 : 6 3 : 4

Weight G f acid formed. 0.572 0.513 0.421 0-456 0.855 0'8E9 0.774 0-887 0 -825 1 *055

Calcu1at)ed as chloro-

nit lo toluene. 0.487 0'437 0.358 0.387 0-728 0'731 0,659 0,755 0.702 0.898

M. p. of acid. - Found. Correct.

126-138" 140-143" 190-155 161 170-220 235

175-180 179 115-130 137-138

155-163 185-186 145--150 148-149 138--143 142-144

165-180 178-180 150-158 165

Weight of unchanged substance.

0.194 0'318 0.448 0.429 0.149 0.170 0'261 0.177 0.266 0.076

Total. 0'681 0.755 0'806 0'816 0.877 0.901 0.920 0.932 0.968 0.974

The following table shows the amount of hydrochloric acid set free by the ortho-nitro-compounds compared with the 3 : 5 and 3 : 4 chloronitrotoluenes.

SERIES V.-Oxidation of the Chloronitrotoluenes.

Time, 5 hours. Temperature, 11 9-1 2 2 O . Hytlro-

Woigli t Weight chloric Weight Calcu- of un- of acicl calcu-

of lated as M. p. of acid. changed changed lated as acid chloronitro- 7- sub- + u11- chloronitro-

NO, : C1. formed. toluene. Found. Correct. stance. changed. toluene. Total. 2 : 3 0'185 0.157 180-220" 235" 0.696 0.853 0'046 0.899 2 : 5 0.220 0.187 115-130 137-138 0 7 4 7 0'933 0'049 0.982 2 : 6 0'258 0'219 130-155 161 0.697 0.916 0.055 0.971 2 : 4 0'440 0.374 120-135 140-143 0.526 0'898 0'099 0.997 3 : 5 0'289 0'246 140-146 148-149 0.722 0'968 0'010 0 978 3 : 4 0.729 0'620 165-175 178-180 0.359 0.979 0'009 0.988

The amount of chlorine set free from the nucleus appears to Fear a n approximately constant ratio to the quantity of substance oxidised as seen from the following table.

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974 COHEN AND HODSMAN: OXIDATION OF THE NITRO- AND

Weight of HC1 calculated as Weight of

NO, : CI. chloroi~itroteluene. acid formed. lta tio. 2 : 3 0'046 0.185 0.25

0.055 0.258 0.21 Series V ~

Series IV 2 : 4 0.165 0'689 0.24

\ 2 : 5 0-049 0'220 0'22

i 2 : 4 0'099 0'440 0.22

From this it appears probable that the action on the nucleus and on the side-chain are closely related, or, in other words, that the second change depends on the first.

EXPEBIM ENTAL.

Several of the compounds used in the foregoing experiments were prepared by special methods. The 3-chloro-2-nitrotoluene has not been previously described and was first obtained by one of us in conjunction with Mr. H. G. Bennett, so that all the ten isomeric chloronitrotoluenes are now known. I n the preparation of the 5-chloro-2-nitrotoluene, Noelting and Stocklin's method (Ber., 1891, 24, 564) was found unsatisfactory and was accordingly modified.

3-ChZoro-2-nitrotoZuene.-2 : 6-Dinitrotoluene mas reduced to 2 : 6-nitrotoluidine in the usual way and the basic group acetylated. Ten grams of the nitroacetotoluidide were dissolved in 30 C.C. of hot glacial acetic acid, and dry chlorine was a t once passed into the solution which was not allowed to cool. I n this way chlorination proceeds without any crystallisation of the original substance. When the increase in weight roughly corresponded to the substitution of one atom of chlorine the process was stopped. After standing overnight, some of the chlorinated product usually separated out ; otherwise crystallisation was hastened by cooling the solution in ice and salt. These crystals, which were not very pure (m. p. 110-125°), were filtered off and a further quantity of chlorinated product wits obtained as an oil by the addition of water to the filtrate. The oil partially solidified to a viscid mass from which the substance way obtained by repeated extraction with boiling water. The crude product was crystallised from alcohol and finally from water and melted a t 150-152'. On analysis :

0.2607 gave 0.1610 AgC1. C1= 15.28. C,H9O,N,C1 requires C1= 15.54 per cent.

By heating the substance in a sealed tube with five times its weight of concentrated hydrochloric acid the acetyl group was removed, and the amino-group was then replaced by hydrogen by the usual method of diazotising in alcohol. The product mas purified by draining it for several hours on a porous plate, cooied in ice, and then melted at

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CHLORO -DERIVA'l'IVES OF TOLUENE. 9'75

22-23O. The yields were very small. The constitution of the chloronitrotoluene was determined as follows, The acetyl derivative of the chloronitrotoluidine was hydrolysed and the amino-group replaced by chlorine. The product was then nitrated and gave a dichlorodinitrotoluene melting at 1OO-l0lo. Now, according to Cohen and Dakin (Trans., 1901, 79, 1129, 1131) this melting point corresponds to the 2 : 5-dichlorodinitrotoluene and not to the 2 : 3-dichloro-compound, m. p. 71', which is the only other likely product. The chlorine therefore entcrs the ortho-position t o the nitro-group, the reactions taking place as follows :

Me Me M0

O , N ( ' ~ N H A ~ -+ O,N/\NHA~ C1l I --+ o ZCll N/)NH -+ \/ \/

(153") (95") \/ (1 60')

Me

(6 8-7 0') ( 1 0 1 O ) .

The melting points of the diiferent compounds are given with the respective formulae.

In addition to the above, a dinitro-derivative of the chloronitro- toluene was prepared melting at 68-70' and a benzoyl derivative of the chloronitrotoluidine which melted a t 212-21 3".

In the preparation of the chlorine derivative of the nitroacetotoluidide the process of chlorination should not be prolonged; otherwise a second hydrogen atom may be replaced by chlorine.

In one experiment 5 grams of the 3-nitro-6-acetotoluidide dissolved in 10 C.C. of hot glacial acetic acid were kept at 100' for five hours during which time dry chlorine was passed into the solution. The product was separated by cooling in ice and salt, and by adding a little alcohol. I t was recrystallised from alcohol and melted at 195-197" :

0.3282 gave 0.3528 AgCI.

The formula of t.hs dichloro-compound is probably

C1= 26-67. C911,0,N2C12 requires C1= 26.99 per cent.

Me

O,N/\NHA~. Cl(,Gl

5-ChZoro-2-nitrotoZuene.-m-Toluidine was acetylated with acetic anhydride and the product freed from the anhydride by allowing

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976 OXIDATION OF NITRO- AND CHLORONITRO-TOLUENES.

it to stand in contact with dilute sodium carbonate solution, for other wise the subsequent nitration does not proceed smoothly.

To two parts of m-acetotoluidide dissolved in two parts of glacial acetic acid and eight parts of concentrated sulphuric acid cooled below 20°, one part of fuming nitric acid was gradually added, the tomper- ature being kept a t 5-10", The nitro-group enters the para-position and, to a less extent, the ortho-position to the amino-group. The product was immediately poured into water, which precipitated the nitro-compounds.

The acetyl group was removed by heating the product on tlie mater- bath with dilute sulphuric acid (1 vol. H,SO,: 1 vol. water) until all had passed into solution. After neutralising the acid with sodium carbonate the base was distilled with steam to remove the 4-nitro- m-toluidine which is more volatile than the 2-nitro-compound. When the melting point of the distillate became constant, the residue was filtered, washed, and crystallised from alcohol (m. p. 135-138').

The amino-group was replaced by chlorine, giving 5-chloro-2-nitro- toluene which was purified by distillation under reduced pressure :

0.2968 gave 0.2502 AgCl. C7H,0,NC1 requires Cl = 20.69 per cent.

The remaining isomerides were obtained by well-known methods. Details of the results obtained by the oxidation of Series I and I1 of

C1= 20.85.

the chloronitrotoluenes are given in the following tables.

SERIES I.-Oxidation of the Chloronitrotoluenes.

Time, 2 hours. Temperature, 130-140°.

NO, : c1. 2 : 3 3 : 2 2 : 4 4 : 2 2 : 5 5 : 2 2 : 6 3 : 4 4 : 3 3 : 5

Acid formed.

0.111 0.286 0'314 0.288 0.1 32 0.21 1 0.160 0 '534 0'206 0.213

Calculated as chloro-

nitrotoluene. 0.095 0.243 0.267 0.245 0.112 0.180 0'136 0'454 0.252 0.181

31. p. of acid. - Found. Correct.

180-195" 235" 175-180 179 125-135 140-143 135-140 142-144 122-132 137-138 155--161 165 140-155 161 175-180 185 137-141 178-180 145-148 148-149

Unchanged SubstallcP.

0.873 0.655 0-668 0'782 0.836 0.812 0.828 0.515 0.719 0.812

Total. 0 968 0'898 0.935 1 -027 0.948 0.992 0 964 0 960 0 .9 i l 0.993

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CYANODIHYDROCARVONE DERIVATIVES.

SERIES 11.-Time, 24 hours. Temperature, 1 30-140".

NO, : Cl. 2 : 3 3 : 2 2 : 4 4 : 2 2 : 5 5 : 2 2 : 6 3 : 4 4 : 3 3 : 5

Acid fo r l l lod .

0.103 0'530 0.542 0-583 0 3 1 6 0-436 0.327 0.672 0'634 0.432

THE UNIVEI~SITY, LEEDS.

Calculated as chloro-

11 i tro to I uenc. 0.088 0.451 0'461 0.496 0.269 0.371 0.278 0.572 0 540 0.368

&I. 1). of acid. - Foond. Correct.

185-200" 235" 177-181 179 124-136 140-143 135-140 143-144 123-134 i37--138 157-161 165 145-155 161 170-177 178-180 136-141 155-186 146-149 148-1 49

Uncliaiiged snbstancr.

0'859 0'460 0.383 0'486 0'646 0.565 0.639 0.279 0.403 0.584

97 7

Total. 0.957 0.911 0,844 0.982 0.915 0'936 0.917 0,851 0.943 0-952

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