CHEMISTRY

THE CHEMISTRY OF ACETYLENIC ETHERS

BY

J. F. ARENS AND P. MODDERMAN

(Communicated at the meeting of Sept. 30, 1950)

PART. I.

Review of known reactions.

Relatively few publications deal with the reactivity of acetylenic ethers. a. The acetylenic hydrogen atom is mobile and can be exchanged for

metal atoms by means of a GRIGNARD compound or another suitable reagent 1). The magnesium and lithium derivatives behave like ordinary GRIGNARD reagents and react for instance wi~h carbonyl compounds 1.2).

HC = COC2H 5 + C2Hs Mg Br -+ Br Mg C = COC2Hs + C2Hs

/ OH R -C = 0 + Br Mg C = COC2Hs --+R -C-C = COC2Hs

I 2 steps I R' R'

I

b. The acetylenic ethers are. easily hydrated by means of acidified water yielding esters 3

a).

H+ / 0 HC = COC2Hs + H 20 --+ H3C-C~

OC2H s

This property belongs also to the derivatives without an acetylenic hydro­gen atom. So I can be transformed into an a, p-unsaturated ester 3b

).

/OH H+ / 0 R-C-C = COC2Hs --+ R-C = CH-C~

I (H20) I OC2Hs R' R'

c. Alcoholic HCI and ethoxyacetylene give ethylacetate and ethyl­chloride 4).

HCI + C2HsOH + HC - COC2Hs -+ C2HsCI + CH3COOC2H s

d. Dry hydrogen chloride in ether gives ethyl-a-chlorovinyl-ether IC).

_ / OC2H s HC = COC2Hs + HCI -+ H 2C = C~

Cl

This substance reacts violently with water to yield ethylacetate.

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e. Alcohol can be added to the triple bond under the influence of boron­fluoride.

The primary product is an ortho ester which decomposes under the influence of the catalyst into an ether and an acetate Ib).

BF3 HC = COC2Hó + 2 C2HóOH ~ H aC-C(OC2Hó)s

BFal C2H óOC2H ó + CHSCOOC2Hó .--

f. The acetylenic triple bond can be partially hydrogenated by means of a Pd catalyst giving a vinyl ether which in turn can be hydrolysed to an aldehyde (compare ref. 2/).

Hl /H HIO /H R-C = COC2H ó Pd~ R-CH = C'" -~ R-CH2-C"

OC2H ó H+ 0 + C2HsOH

g. On storing the acetylenic ethers polymerise slowly yielding complex mixtures 1.5). On heating the ethers may explode I).

h. For halogen derivatives of phenoxyacetylene see ref. 6. With the aim of extending the know1edge of the chemistry of the

acetylenic ethers, we are engaged in the study of the action of various organic compounds on ethoxyacetylene.

PART 11.

Formation of anhydrides in the reaction of ethoxyacetylene with anhydrous carboxylic acids.

Summary.

Ethoxyacetylene HC = C - OC2Hs reacts with saturated and unsatur­ated aliphatic and aromatic acids under the formation of the anhydride of the acid and ethylacetate. With formic acid ethylacetate and carbon monoxide are formed. In these reactions ethoxyacetylene thus behaves like a powerful dehydrating agent.

Considering the reaction mentioned in part I point d, it might be expected that upon addition of organic acids to ethoxyacetylene one would obtain vinylderivatives like 11.

/OC2H ó

HC = COC2H ó + HOOC-R ~ H 2C = C'" OCOR

11 (Reaction A).

We observed however that each molecule of ethoxyacetylene reacts with two molecules of the acid. The net result is the formation of ethylacetate

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and the anhydride of the acid. This transformation proceeds without the addition of a catalyst.

In the case of formic acid, the reaction takes a somewhat different course as the anhydride of this acid, is unstable. We observed a vigorous evolution of carbon ' monoxide upon the addition of ethoxyacetylene to an ethereal solution of 2 moles of anhydrous formic acid. One mole of the acid remained unchanged. The only other product of the reaction was ethylacetate.

It is probable that the reactions with the acids occur in two steps. The first (Reaction A) results in the formation of a vinyl compound (II) a derivative ofketene, which, ex cept in the case offormic acid, reacts further with another molecule of the acid according to reaction B, the hypo­thetical intermediate substance III being unstable.

II III

Reaction B

In order to obtain the substance II (R=CH3) as the main product of the reaction, we slowly added ace tic acid to a large excess of ethoxyacetylene. However we again obtained ethylacetate and acetic anhydride, while a considerable part of the ethoxyacetylene remained unchanged. This result can be explained by assuming that the reaction rate of B is much faster than of A, so that any II formed immediately reacts with acetic acid. The reactions as described above, are analogous to the reactions of acetylene with organic acids 7) altough these require catalysts like boronfluoride and mercuric oxide or strong acids and a mercuric salt.

HC = CH + CH3COOH -+ H2C = CH-OCOCH3 IV

/H IV + CH~COOH -+ H3C -C"" OCOCH3

OCOCH3

/ H -+ H3C-C~ + CH3CO-0-COCH3.

'\ 0

The formation of anhydrides in the reaction of ethoxyacetylene with carboxylic acids seems to be general, as also aromatic and unsaturated acids give similar results. Even non carboxylic acids such as picric acid

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react with ethoxyacetylene, though the reaction takes a somewhat different course. This will be published in a following paper.

Our thanks are due to Mr Yo KIM TEK for valuable assistance in the laboratory.

Experimental part 1).

a. Reaction ot etkoxyacetylene witk 2 'TTWles ot acetic acid.

To 13 g of glacial acetic acid was added under stirring a solution of 7,5 g of ethoxyacetylene in 20 cm3 of absolute ether. The mixture became warm. Af ter the complete addition it was refluxed for I hr. and subsequently distilled fractionally by means of a 20 cm column packed with glass helices. Mter a fore running of ether we obtained 7I g of ethylacetate (bp. 74°) and 7 g of acetic anhydride (bp. 125 - 133°). Residue 31 g.

b. Reaction ot acetic acid witk a large excess ot ethoxyacetylene . .

4,5 g of glacial acetic acid dissolved in 15 cm3 of abs. ether was added very slowly to 14,5 g of ethoxyacetylene. The temperature was kept at 40°. Mter standing for 1 night at roomtemperature (20 - 25°) the solution was fractionally distilled using a 20 cm column packed with glass helices. We 0 btained the following fractions:

33 - 60° 16,0 g mixture of ether and ethoxyacetylene (b.p. ethoxy­acetylene 51°).

60 - 72° 1 g ethylacetate. The distillation was continued in vacuo (25 mm); between the pump and the receiver a cold trap was used.

52 - 53° (25 mm) 2,0 g acetic anhydride. residue 0,5 g. The cold trap contained 21 g of ethylacetate.

c. Reaction ot etkoxyacetylene witk butyric acid.

To 36,3 g of butyric acid was slowly added 14I g of ethoxyacetylene in 25 cm3 of ether. Heat was evolved. Af ter standing for i hr. the mixture was fractionally distilled using a 20 cm column packed with helices. Mter a fore running of ether we 0 btained 13 g of ethylacetate bp. 65 - 74° (main part distilling at 74°), then, in vacuo, 18 g of a fraction bp. 85 - 105° (34 mm) consisting of butyric acid and butyric anhydride and finally 121 g of butyric anhydride bp. 105 - 106° (34 mm). The residue weighed . II g. The cold trap between the pump and the receiver contained 2I g of ethylacetate.

d. Reaction ot etkoxyacetylene witk benzoic acid. An absolute ethereal solution of 7 g of ethoxyacetylene in 35 cm3 of

ether was added to 24,4 g of benzoic acid. The mixture was refluxed for . 3 hrs. The acid gradually dissolved and the odour of the ethoxyacetylene

1) Unless otherwise stated all distillations were carried out at 700 mm, the ordinary pressure at Bandung. .

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disappeared. A rather large amount of benzoic acid was however un­changed. On cooling to - 10° it separated (7! g). The filtrate was slowly distilled through a 20 cm column packed with glass helices. Af ter a large forerunning of ether we obtained a fraction bp. 70 - 72 consisting of ethyl acetate (l! g). This yield is rather low but can be explained by considerable losses during the distillation. A part of the acetate is entrained with the fore runnings and a part remains in the residue. The residue was dissolved in ether and washed with ice cold 5 % sodiumhydroxide. (Upon the addition of hydrochloric acid thc aqueous layer yielded 6,7 g of benzoic acid). The ethereal extract was dried and evaporated and left a residue of 9! g of benzoic anhydride (mp. 41 - 42°).

e. Reaction ol etkoxyacetylene witk lormic acid.

To a solution of 19 g of 98 - 100 % formic acid in 20 cm3 of abs. ether was dropped under stirring but without cooling, a mixture of 14 g (0,2 mole) of ethoxyacetylene and 35 cm3 of ether. ' A large amount of gas evolved (about 5 liters). This proved to be carbon monoxide. Af ter the reaction was complete a sample was titrated with 0,1 n sodium hydroxide. 0,263 mole of acid had remained, so that 0,150 mole had reacted with the ethoxyacetylene. The reaction mixture was washed with water, neutralised with sodium carbonate and distilled. We obtained 12! g of ethylacetate (bp. 74°).

I. Reaction ol etkoxyacetylene witk cinnamic acid.

A solution of 7! g of ethoxyacetylene in 12 cm3 of ether was added to 10 g of dry, finely powdered cinnamic acid. The mixture was refluxed under stirring for 2 hrs. The acid gradually dissolved. Af ter standing overnight a crystalline solid was formed. This had a mp. of 130 - 134° and gave no depression of the mp. with the anhydride of cinnamic acid (mp. 136°). Yield 71 g. The filtrate was distilled and yielded a fore-running of ether and then 2,3 g of ethylacetate. The residue crystallised and weighed 2 g.

g. Reaction ol etkoxyacetylene witk (trans) crotonic acid. A solution of 7! g of ethoxyacetylene in 12 cm3 of ether was added to

14 g of crotonic acid. The reaction started af ter heating to 40°. The mixture was refluxed for li hrs. and then fractionally distilled by means of a 20 cm column packed with glass helices. Af ter a fore running of ether we obtained 51 g of ethylacetate bp. 71 - 74°. Distillation was continued in vacuum (25 mm). Between the pump and the receiver we used a trap cooled in ice salt, in order to condense the remainder of the ethylacetate. The boiling point at on ce rose to that of crotonic anhydride (135 - 140°, 25 mm). Yield 101 g. Residue 1 g. The trap contained 2 g of ethylacetate.

Laboratory ol Organic Chemistry University ol lndonesia July 1950. Bandung Java.

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1. a. JACOBS, TH. L., R . CRAMER, F. T. WEISS, J. Am. Chem. Soc. 62, 1849 (1940). b. , J. S. HANSON, J. Am. Chem. Soc. 64, 223 (1942). c. FAVORSKI, A. E. and M. N. SHCHUKINA, J. Gen. Chem. U.S.S.R. 15, 394

(1945). 2. See for instanee J. F. ARENs, D. A. VAN DORP, Rec. Trav. Chim. 67, 973 (1948). 3. a. JACOBS, TH. L. and S. SEARLESS, J. Am. Chem. Soc. 66, 686 (1944).

b. HEILBRON, 1. M., E. R. H. JONES, M. JULIA and B. C. L. WEEDON, J. Che~. Soc. 1823 (1949).

4. FA VORSKI, A. E. and M. N. SHCHUKINA l.c. 5. JACOBS, TH. L. and W. P. TuTTLE, J. Am. Chem. Soc. 71, 1313 (1949). 6. and W. J. WHITCHER, J. Am. Chem. Soc. 64, 2635 (1942). 7. Reviewed by J. A. NIEUWLAND and R. R. VOGT in "The Chemistry of

Acetylene", p. 129-132, (Reinhold Publishing Corporation 1945).