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
COC 2H 5
R -C = 0
I
R'
+ C2H s Mg Br -+ Br Mg C =
COC2H s + C2H s
/ OH
+ Br Mg C = COC H s --+R -C-C =
2
I
R'
2 steps
COC 2H s
I
b. The acetylenic ethers are. easily hydrated by means of acidified
water yielding esters 3a ).
/ 0
H+
HC
= COC H s + H 0 - - + H3C-C~ OC H
2
2
2
s
This property belongs also to the derivatives without an acetylenic hydrogen atom. So I can be transformed into an a, p-unsaturated ester 3 b).
/OH
H+
/ 0
R-C-C
COC2 H s - - + R-C = CH-C ~
I
(H 20)
I
OC 2H s
R'
R'
=
c. Alcoholic HCI and ethoxyacetylene give ethylacetate and ethylchloride 4).
HCI
d.
+ C H sOH + HC 2
COC2H s -+ C2H sCI
+ CH3COOC H s
2
Dry hydrogen chloride in ether gives ethyl-a-chlorovinyl-ether IC).
_
HC = COC 2H s
/ OC 2H s
+ HCI -+ H C = C ~
2
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).
HC
= COC H
BF3
+ 2 C2H óOH ~ H aC-C(OC2H ó )s
BFal
C2H óOC2H ó + CHSCOOC2H ó . - 2
ó
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 /).
R-C
= COC H
2
ó
Hl
/H
Pd~ R-CH = C'"
OC2H ó
HIO
/H
-~ R-CH 2 -C"
H+
+
0
C2H sOH
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 - OC2H s 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.
HC
=
/OC 2H ó
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.
III
II
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
IV
=
CH + CH3COOH
-+
H 2C = CH-OCOCH3
IV
/H
+ CH~COOH -+ H 3C -C"" OCOCH3
OCOCH 3
/ H
-+ H3C-C~
'\ 0
+ CH3CO-0-COCH3.
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
1166
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.
After 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. After 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. After 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 cm 3 of ether. ' A large amount of gas
evolved (about 5 liters). This proved to be carbon monoxide. After 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. After 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 after 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. After 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.
July 1950.
Laboratory ol Organic Chemistry University ol lndonesia
Bandung Java.
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1. a. JACOBS, TH. L., R . CRAMER, F. T. WEISS, J. Am. Chem. Soc. 62, 1849 (1940).
2.
3.
4.
5.
6.
7.
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).
See for instanee J. F. ARENs, D. A. VAN DORP, Rec. Trav. Chim. 67, 973 (1948).
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).
FAVORSKI, A. E. and M. N. SHCHUKINA l.c.
JACOBS, TH. L. and W. P. TuTTLE, J. Am. Chem. Soc. 71, 1313 (1949).
and W. J. WHITCHER, J. Am. Chem. Soc. 64, 2635 (1942).
Reviewed by J. A. NIEUWLAND and R. R. VOGT in "The Chemistry of
Acetylene", p. 129-132, (Reinhold Publishing Corporation 1945).