CATALYTIC REDUCTION OF CARBONYL- AND HYDROXY-

CONTAINING FURAN COMPOUNDS

(UDC 542.97)

N. I. Shuikin, I. F. Bel ' sk i i , and O. N. Savekina

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences, USSR Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 534-537, March, 1964 Original article submitted October 3, 1962

We here report an investigation of the vapor-phase ca ta ly t ic hydrogenation of furan ketones and alcohols con- taining functional groups adjacent to the furan ring. With regard to the former we set ourselves the prac t ica i task of synthesizing d i - and t r i - a lky l homologs of furan from them, for we had previously found the conditions for smooth vapor-phase reduction over skele ta l C u - A 1 for the case of the simpler furan ketones [1]. With regard to furan a lco - hols, our task consisted essentially in obtaining further comparat ive data on their behavior toward plat inum and skele. tal N i - A 1 catalysts, in as much as these catalysts have been investigated previously for the hydrogenation of furan alcohols with a different position of the hydroxy group in the side chain and also for the hydrogenation of furan ke- tones of analogous structure [2-4]. The furan ketones (I) are reduced smoothly in 90-95% yield into the correspond- ing furan homologs (II) when hydrogenated over a skeletal copper-a luminum catalyst in a flow system at 220*:

2 H~, Cu--Al+

C 0 C--C--C C O C--C-- C TI O

(I) (If)

R R

C 0 C --C C 0 C - - C II

0 (D (ID

R = CHs, C~H5

The fu~an alcohols - a -methyl fur fury l a lcohol (III, R = CH a) and c~-ethylfurfuryl a lcohol (III, R = C~H 5) - on hydro- genation by the flow method over P t - C or skele ta l N i - A 1 were first reduced to 2-ethylfuran (IV, R = CH a) and 2- propylfuran (IV, R = C2H5), respectively, and then these products underwent hydrogenolysis at the C - O bond over P t - C and conjugated hydrogenolysis over a skeletal N i - A 1 catalyst . As a result the products of the hydrogenation of a -a lky l fur fury l alcohols contained 2-alkylfurans (35-50%) and al iphat ic ketones (40-50%).

H--R ,., 220 ~ ~ CH2R ~- C--C--C--C--C--R " II

OH O (',;,~) R = CH~, C2Hs (IV) : / =c-c-c--~ =C-R

H--R 220 ~ :~ -. CHaR C--C-- --C--R

OH ( i v ) (Ill) R=CH~ C2Hs C--C--C--R

' ' II 9

496

TABLE 1. Properties of Furan Ketones and Alco -

hols

Furan ketones and B.p. , ~ n~ ] a 20 alcohols (p, ram) !

- , . 5 0 3 2 039 6 8 - 7 0 ( a )

Go t .4962 t .0427

/ ~ii If\

c / N o / ~ - c 64(4) o

=__/C--~ ] C / t O it / \ c - c 66--68 (4) t.4959 t .0t35 rl

o

h lk \ o / \ ~ - c 76--77 (23) i .4800 i .0780

oK

II II \o/\c--c-c 73--75 (8) t.~786 t.0492

The results of the present investigation in conjunc- tion with those of our previous work lead to the general conclusion that the primary reduction of the hydroxy group

is determined by the effect of the furan nucleus inasmuch as only a hydroxy group that is ad jacent to the furan ring can be reduced. As shown previously, in furan alcohols in which the hydroxy group is in the third position in the side chain with respect to the furan nucleus,hydrogenation over P t - C and skeletal N i - A 1 leads oniy to the primary hydro- genolysis of the furan ring with preservation of the hy-

droxy group [2, 3].

The nature of the catalyst does not have a specific influence on the primary react ion of the reduction of the hydroxy group, but it has a substantial effect on the sub- sequent reactions of hydrogenation and the hydrogenolysis of the furan ring. Catalysts for this react ion vary in nature: Group VIII metals supported by charcoal ( P d - C [5], P t - C ) , ske!etal catalysts (Cu-A1 [1]; N i - A 1 , N i - Z n [6]; Pd-A1 [7]), and metals on oxides (Ni -ZnO [8]). Confining our - I t 1 selves to the pecul iar i t ies of P t - C and skele ta l N i - A 1 catalysts, we will refer to one other feature. If furan ke-

tones in which the carbonyl group is adjacent to the furan ring are hydrogenated over these catalysts under conditions s imilar to those for the hydrogenation of furan alcohols, then as well as the primary reduction of the C = O group there occurs (mainly over P t - C ) the primary hydrogenolysis of the furan ring with preservation of the ca~bonyl group [4]. There is therefore an essential difference in the behaviors of catalysts toward the furan ring, on the one hand, and the carbonyl and hydroxy groups, on the other. This question, however, is compl ica ted by the effect of the nature of the catalyst , which shows up very c lear ly here: for example , over skeletal C u - A 1 both furan ketones and furan alcohols containing functional groups adjacent to the furan nucleus undergo only one primary react ion - reduction to the cor- responding furan homologs [1].

E X P E R I M E N T A L

Ethyl 5 -me thy l -2 - fu ry l ketone was prepared by the react ion of 2-methylfuran with propionic anhydride in pres- ence of phosphoric acid [9]. 8 - A l k y l - 5 - m e t h y l - 2 - f u r y l methyl ketones were synthesized via pyryl ium salts by Balaban and Nenitzescu's method [10].

c t -Methyl - and ct-ethyl-fuffuryl alcohols were prepared by the Grignard react ion from 2-furaldehyde and the corresponding alkyl halides. Table 1 lists the properties of furan ketones and alcohols.

Skeletal C u - A 1 and N i - A 1 catalysts were prepared from alloys of copper and nickel with a luminum by remov- al of the a luminum by leaching with 10% NaOH solution, which was added in portions to smali pieces of the al loy. Much heat was evolved, which caused the liquid to boil. After the addit ion of the whole of the a lka l i solution, which was sufficient to remove about one-ha l f of the aluminum, the react ion mixturewas boiled for 4-5 h. The cata lys t was washed with water to remove a lka l i (test with phenolphthalein), and i t was introduced into the react ion tube in the moist state. It was then heated to 200 ~ and hydrogen was passed over i t for 5-6 h.

The pla t inum catalyst was prepared by impregnat ing ac t iva ted birch charcoal with chIoroplatinic acid solution.

It was then placed in the reaction tube and reduced with hydrogen for 15 h, first at 250 ~ and then at 300 ~ The cata lys t contained 10% of plat inum.

Hydrogenation of furan ketones and alcohols. Furan ketones and alcohols were hydrogenated by the flow method by passing their vapors in admixture with hydrogen over catalyst heated to 220 ~ The substance was fed into the re- act ion tube from an au tomat ic buret at a space veloci ty of 0.1 h "1. The ca ta lyzates were separated from water, dried with ca lc ium chloride, and fract ionated through an eff icient column. Fractions corresponding to furan homologs were redist i l led over sodium from a flask fi t ted with a column. The properties of the furan homologs are listed in Table 2. For the properties of the a l iphat ic ketones see [11].

497

TABLE 2. Properties of Furan Homologs

Furan homolog

tl II N o / \ c - c

II [I \ o / \ c - c - c

II /li\ c / N o

C--C--C /c

I} IL. c / \ o / \ c - - c

/ c - c

LI ~ C / N o / \ c - c

B" P" ~ { at 750 mm

91--92

t14--115

t37--t39

t35--137

t50--15t

@

t.4402

1.44t2

1.4464

t.4488

t.4495

20 d 4

0.90i8

0.8876

0.8829

0.893t

0.8837

M R

found

28.1t

32.78

37.5t

37.28

~1.90

calc.

28.42

33.03

37,65

37.65

42.27

SUMMARY

1. 2-Acylfuran homologs were reduced in yields of up to 95% to the corresponding furan homologs by hydro- genation by the flow method over skeletal Cu-A1 at 220 ~ In this way we prepared: 2-methyl-5-propylfuran, 2- ethyl-3,a-dimethylfuran, and 2,3-diethyl-5-methylfuran.

2. On hydrogenation over P t - C or skeletal Ni-A1 by the flow method at 220 ~ a-alkylfuffuryl alcohols are first reduced to the corresponding 2-alkylfurans, and the latter then suffer hydrogenolysis at the C - O bond over P t -C and conjugated hydrogenolysis over skeletal Ni-A 1 with formation of aliphatic ketones.

L I T E R A T U R E C I T E D

1. N . I . Shuikin and I. F. Bel'sldi, Dokl. AN SSSR, 127__._, 359 (1959). 2. I .F . Bel'sldi and N. I. Shuikin, Dokl. AN SSSR, 128, 945 (1959). 3. N . I . Shuikin and I. F. Bel'skii, Dokl. AN SSSR, 13__.1_1, 109 (1960). 4. I .F . Bel'skii, Izv. AN SSSR. Otd. khim. n., 1962, 142. 5. N . I . Shuikin and I. F. Bel'skii, Dokl. AN SSSR, !17, 95 (1957). 6. N . I . Shuikin and I. F. Bel'skii, Zh. obshch, khimii, 2__9_9, 3627 (1959). 7. N . I . Shuikin and I. F. Bel'skii, Dokl. AN SSSR, 125, 348 (1959). 8. N . I . Shuikin and I. F. Bel'skii, Izv. AN SSSR. Otd. khim. n., 1958, 506. 9. .4. L. Mndzhoyan, Syntheses of Heterocyclic Compounds [in Russian], No. 2, Izd. AN ArmSSR, Erevan (1958),

p. 14. 10. A . T . Balaban and K. D. Nenitzescu, J. Chem. Soe., 1961, 3553; Bet. 93, 599 (1960); Liebigs Ann. Chem.,

625, 74 (1959). 11. N . I . Shuikin and I. F. Bel'skii, Zh. obshch, khimii, 26, 2716 (1956).

All abbreviations of periodicals in the above bibliography are letter-by-letter transliter-

ations of the abbreviations as given in the original Russian journal. Some or all of this peri-

odical l i t e ra ture m ay we l l be a v a i l a b l e in E n g l i s h t rans la t ion . A c o m p l e t e l i s t o f t h e c o v e r - t o -

c o v e r E n g l i s h t r a n s l a t i o n s a p p e a r s a t t h e b a c k o f t h i s i s s u e .

498