Nov., 1947
ESTERFORMATION IN THE ALCOHOLYSIS OF IMINOESTER HYDROCHLORIDES 2663
Anal. Calcd. for lCloHm04: CeHsO, 88.2; C, 58.8; H , C, 58.0; H , 9.70. 9.87. Found: C ~ H S O85.8; , The petroleum ether insoluble portion of the reaction mixture wa5 covered with toluene and treated with water to liberate ethyl alcohol from the sodium ethoxide produced in the reaction. The water layer was saturated with potassium carbonate and the organic layer was separated. The mixture of organic compounds was distilled and everything collected until pure toluene started to distil. The distillate, when treated with 3,5dinitrobenzoyl chloride, yielded 10.7 g. of ethyl 3,5dinitrobenzoate. This corresponds to a 235% yield of alcohol from the reaction bet ween pentaethoxyethane and sodium ethyl to produce ethane, sodium ethoxide and VI. Tetraethoxyethylene absorbs bromine rapidly with the formation of diethyl oxalate and, presumably, ethyl bromide. No attempt was made to isolate the latter compound. Treatment of the diethyl oxalate so produced with concentrated ammonia gave oxamide, a solid which decomposed without melting when heated to 340' for one minute in a sealed tube and melted with decomposition a t 350" when placed in a copper block a t that temperature. An authentic sample of oxamide, as well as a mixture of
[CONTRIBUTION FROM
THE
this sample with the amide derived from VI, showed t h e same behavior, which is in marked contrast to the melting point of 417-419' dec. reported15 for oxamide in the literature. The diethyl oxalate from VI also was converted to oxalhydrazide by the procedure of Sable; the m. p. of this product was 239-240' dec., as was t h a t of a mixture of this product with a n authentic sample of oxalhydrazide.
Summary Diethoxyacetonitrile has been converted to pentaethoxyethane (ethyl diethoxyorthoacetate). This orthoester reacts with sodium ethyl to give tetraethoxyethylene (diethoFyketene diethylacetal), a colorless liquid, b. p. 195-196', that shows no tendency to dissociate into carbon monoxide diethylacetal as has been reported by Scheibler and co-workers. (15) Michael, Bcr., 28, 1632 (1895). (16) Sah, Rec. fvav. chim., 69, 1036 (1940).
MADISON, WISCONSIN
RECEIVED MARCH22, 1947
LABORATORY OF ORGANIC CHEMISTRY OF THE UNIVERSITY OF WISCONSIN]
Ester and Orthoester Formation in the Alcoholysis of Iminoester Hydrochlorides. A Proposed Mechanism BY s. M. MCELVAIN AND CALVIN L.STEVENS' Orthoesters have been used extensively in this tion of certain a,a-disubstituted orthoesters: the Laboratory as intermediates in the preparation of reaction of the iminoester hydrochloride with ketene acetals, RCH=C(OR')2. When R is alcohol to produce the ester, R2CHCOOR', and alkyl, these acetals are prepared by the action of an ether, R'20. In an attempt to prepare methyl sodium on the corresponding a-bromoorthoesters2; a-phenylorthobutyrate (11, R is C2H6) by the when R is phenyl, the ketene acetals result simply alcoholysis of the iminoester hydrochloride (I) defrom the pyrolysis of the or tho ester^.^ Conse- rived from a-phenylbutyronitrile, none of the quently] a further extension of the study of ketene orthoester could be isolated, although the methacetals, particularly in the direction of the disub- oxy1 content of the products indicated a small stituted compounds R2C===C(ORt)2, necessitated amount had been formed; the main products were the amide I11 together with the ester IV and dithe preparation of the corresponding orthoesters. As previously i n d i ~ a t e dthe , ~ concurrent forma- methyl ether. tion of an amide and CHsOH an alkyl chloride dur+-I CsHsCHRC(OCHJ8 NHdCl ing the alcoholysis of I1 an iminoester hydroCeHsCHRCONHa CHaCl chloride is the chief CsHsCHRC(OCHs)="aCI 111 difficulty that has been I encountered in the CsHsCHRCOOCHa hH4Cl (CH8)ZO preparation of orthoIV esters by the Pinner However, the methanolysis of the iminoester p r o c e d ~ r e . Attempts ~ to eliminate or to minimize this undesired side reaction have been reasonably hydrochloride (I, R is CHs) derived from asuccessful when the orthoester has a single a-sub- phenylpropionitrile gave the corresponding orthostituent, but much less so if the orthoester has ester I1 in 21% yield; accompanying this product was 25% of the amide (111) and 28% of methyl two a - s u b ~ t i t u e n t j . ~ The present paper reports a new complication a-phenylpropionate (IV). An intermediate fracthat has been observed in the attempted prepara- tion, consisting of approximately equal parts of I1 and IV, accounted for the remainder of the re(1) Wisconsin Alumni Research Foundation Research Assistant, action products. 1944-1947. ( 2 ) McElvain, e1 al., ram JOURNAL, 62, 1482 (1940); 64, I966 In'the hope that the formation of amide could (1 942). be prevented, and hence the yield of orthoester (3) McElvain and Stevens, ibid., 68, 1917 (1946). increased, the boron trifluoride coordination com(4) McElvain and Fajardo-Pinzon, ibid., 67, 690 (1945) pound of methyl a-phenyliminopropionate (V) (5) Pinner, Bcv.. 16, 356, 1644 (1883).
j
+ +
+
s. M.MCELVAINAND CALVINL.STEVENS
2664
Vol. 69
was prepared and subjected to alcoholysis. This compound obviously cannot undergo pyrolysis to the amide as does the hydrochloride salt (I). No amide was produced in the methanolysis of V; the reaction products were the ester IV, dimethyl ether and boron fluoride-ammonia
scribed appear to be unrelated to any of the previously observed reactions by which such esters are produced. The formation of the esters (IV) and ether occura during the alcoholysis of the iminoester hydrochloride and is not the result of decomposition, either thermal or catalyzed, of the orthoesters. The orthoester (11, R is CHs) is CHaOH C&CH ((>Ha)C (OCHJ=NHBFs -+ quite thermostable during fractional distillation V IV (R is CHI) HaN-BFI (CH&O and the fact that the yields of I1 are not noticeThese products formed so readily i t appeared that ably affected by making the alcoholysis mixture the boron fluoride-ammonia had catalyzed the basic with sodium methoxide before distillation, decomposition of the orthoester as rapidly as i t indicates that the orthoester is not catalytically was formed. This seems likely from the fact that decomposed by an acidic salt in the reaction mixan otherwise stable orthoester, methyl ortho- ture as was the case with pentaethoxyethane: butyrate, was smoothly converted to methyl buty- Also, dimethyl ether can be isolated from the rate and dimethyl ether when heated in methanol alcoholysis mixture after i t had stood a t room temsolution with a catalytic amount of boron fluoride- perature for one day. These facts indicate that the formation of the ester (IV) and ether is indeammonia. The isolation of some of the ester, ethyl phenyl- pendent of and takes place concurrently with the acetate, has been reported0 in the preparation of production of the orthoester (11). A factor which appears to have a significant phenylketene diethylacetal by the pyrolysis of the alcoholysis product from ethyl phenyliminoacetate effect on the amount of orthoester produced in hydrochloride. This ester was showna to be pro- the alcoholysis of I is the size of the substituent R. duced by the thermal decomposition of the ketene When R is H, only the orthoester, methyl orthoacetal with the concurrent formation of ethylene. phenylacetate, is formed (67%) together with a This type of ester formation was prevented when small amount (8y0)of the amide (III)a; ,when R is the corresponding methyl iminoester hydrochlo- CHs the ester IV is isolated in 28% yield and only a 21% yield of the orthoester I1 is obtained. ride was subjected to methanolysis.3 Another case of simple ester formation during When the size of R is increased to CzHs, the ester the alcoholysis of an iminoester hydrochloride re- IV is practically the sole alcoholysis product. These facts are accommodated by the following cently was noted7in this Laboratory in connection with the preparation of pentaethoxyethane. In mechanism, the proposed intermediates of which this case it appeared that the ester (ethyl di- seem necessary to account for the products (amide, ethoxyacetate) and diethyl ether resulted from ester and orthoester) that may be obtained from the decomposition of preformed orthoester. This the alcoholysis of such an iminoester hydrochlodecomposition was shown to be catalyzed by the ride as I.
+
+
R
OCHI
Y+
CHiOH ' _ _ f
C~I~CH-C-NH~CI I
I
R
OCH,
VXa JCHlOH
SH,CI
+ C ~ H ~ C H ~ - - O C H ~C~H~CH-M+CH~ I
I
R
1I'
I
JCHIO-
I1
iminoester hydrochloride and i t could be controlled sufficiently to permit the isolation of some orthoester by making the reaction mixture basic with sodium ethoxide a t an appropriate stage in the alcoholysis. The formation of the esters (IV) during the alcoholysis of the salts (I) in the work now de(6) Stsudingu, and Rathsam, Hero. Cltim. Acto, I,645 (1922). JOURNAL, 89. 2657 (1947). (7)McElvain and Clarke, THIS
1
R
OCHa
\'IIa
OCHa JCHaO-
+
IV (CHshO Regardless of the structure (I or Ia) of the iminoester salt, its acquisition of a proton from the alcohol produces the intermediate (VI and VIa). The postulation of an intermediate resulting from the interaction of I with the alcohol seems necessary to account for the fact that a considerable amount of the amide (111) generally is formed during alcoholysis under conditions (in alcohol solution at room temperature) that are consider-
ESTERFORMATION IN TIIE ALCOIIOLYSIS OF IMINOESTER HYDKOCIILORIDES 266.5
S o v . , 1947
ably milder than those necessary for the decomposition of tlie solid itninoester hydrochloride into the amide and alkyl chloridc. This latter reaction occurs a t the melting point of thc salt N +
-
K#2HC=NH:2Cl I.
+IZ'Cl
+ l
