DECOMPOSITION OF ALKYLCHLOROGLYOXALATES
March 5, 1963
yellow color persisted for 2 minutes. Excess diazomethane and ether was then boiled off and the ester used for epimerization without purification. Epimerization of Xa to Xb.-To a solution of 90 mg. of sodium in 10 ml. of absolute ethanol was added 180 mg. of methyl ester of Xa, and the solution was refluxed for 24 hours. Water ( 5 ml.) was then added dropwise and the mixture was refluxed for an additional 4 hours. The reaction mixture was then diluted with 10 ml. of water and thoroughly washed with ether. The aqueous layer was then acidified with 5 N hydrochloric acid and the precipitate which formed was collected by filtration and dried under vacuum. This was then sublimed (58'; 0.8 mm.) to give 45 mg. of oily liquid which gave an infrared spectrum identical with that of Xb. This oily liquid was dissolved in 5% NaOH and was reprecipitated by acidification with 5 N hydrochloric in a white, crystalline state, m:p. 58". This product showed no depression in m.p. when mixed with X b . It gave an infrared spectrum identical with that of X b . Preparation of Iodolactone XI.-A solution of 508 mg. (0.004 mole) of iodine and 2 g. of potassium iodide in 6 ml. of water was added to 248 mg. (0.002 mole) of I X a dissolved in 12 ml. of 0.5 N sodium bicarbonate solution. The mixture was allowed to stand in the dark a t room temperature for 24 hours. A light yellow crystalline product formed and was separated by fi1tr:tion and air-dried. It amounted to 380 mg. (76y0), m.p. 97-102 . The infrared spectrum of the crude product showed it to be mainly &lactone (5.75 p ) containing a small amount of the 7lactone (5.65 p ) . The &lactone, m.p. 105.5', was obtained in pure state by crystallization from cyclohexane; infrared ( CHC13): 5.75, 6.95, 7.26, 7.37, 7.50, 8.69, 9.11, 9.23, 9.53, 9.80, 10.00, 10.28, 10.47, 11.24, 11.58, 11.91 p . Anal. Calcd. for CiH7021: C, 33.60; H, 2.80; I, 50.80. Found: C,33.42; H, 2.82; I, 50.86. Conversion of Iodolactone XI to Acid 1Xa.-Iodolactone X I (90 mg.) was dissolved in 30 ml. of glacial acetic acid and cooled to
[CONTRIBUTION FROM
THE
585
5'. Zinc dust (400 mg.) previously cooled to 5" was dropped a t once into the iodolactone solution. The mixture was vigorously shaken for 5 minutes and quickly filtered through a bed of Celite (prepared by suspending Celite in acetic acid, filtering and washing with acetone). Acetic acid was removed under vacuum and the residue was dissolved in sodium hydroxide solution, extracted with chloroform and acidified with 5 N hydrochloric acid. The solution was extracted three times with ether. The ethereal layer was dried over anhydrous sodium sulfate and the ether removed on the flash evaporator. The product was purified by c r y s t a l l i z a t p from hexane to give 25 mg. (55%) of pure acid, m.p. 90-91 , which showed no depression in mixed melting point with IXa and gave an infrared spectrum identical with that of IXa. Vapor Phase Chromatography.-Vapor phase chromatography was carried out using a Beckman GC-2 instrument equipped with a 6-ft. Craig polyester column a t 160'. Helium a t a pressure of 20 p.s.i. was used as carrier gas. Compound
Retention time, min.
Methyl bicyclo [3.1.0]hex-2-ene-endo-6carboxylate Methyl bicyclo[3.1 .O] hexane-6-endocarboxylate Methyl cyclohexanecarboxylate Methyl bicyclo[3.1.0]hexane-6-exocarboxylate Pd-C prod. from hydrogenation of IXa
Z .
13.5"
11.0" 7.8" 13.5" 7 . 8 (1st peak) 11.0 (2nd peak) 1 9 . 7 (3rd peak)
No detectable impurity.
DEPARTMENT OF CHEMISTRY, UNIVERSITY OF WYOMING, LARAMIE, WYO.]
Decomposition Reactions of Alkyl Chloroglyoxalates1,2 B Y S A R A JANE
RHOADS AND ROBERT E.MICHEL3
RECEIVED SEPTEMBER 10, 1962
I
Alkyl chloroglyoxalates of structure ROCOCOCl ( R = C2Hs,n-CdHs, 2-CsH17,CsHsCHCH3) decompose smoothly when heated in the presence of pyridine to yield the corresponding alkyl chlorides, carbon dioxide and carbon monoxide. The decompositions of active 2-octyl chloroglyoxalate (IIIc) and active a-phenethyl chloroglyoxalate ( I I I d ) have been studied as pyridine-induced reactions and as thermal reactions. Both IIIc and I I I d undergo the pyridine-induced decomposition to give the corresponding alkyl chlorides with a high degree of inversion of configuration, a result suggestive of an S N process ~ involving the first-formed pyridinium salt. Compound IIIc is resistant toward decomposition when heated alone or in neutral solvents, while IIId decomposes when heated alone or in nitrobenzene to give a-phenethyl chloride with a preponderance of retention of configuration. Relative rates of the first-order thermal decomposition of IIId in tetralin, diglyme and nitrobenzene are 1:2.34: 13.6 a t 108'. I n comparison with the structurally analogous alkyl chloroformates and alkyl chlorosulfinates, the alkyl chloroglyoxalates show an unexpected thermal stability. The mechanistic implications of these findings for the thermal decomposition are discussed in terms of current hypotheses concerning SNi reactions.
Although the advantages of oxalyl chloride as a reagent f o r the conversion of acids to acid chlorides have been recognized for many year^,^ its potentiality as a reagent for the corresponding conversion of alcohols to alkyl chlorides appears to have been neglected.6 In order t o explore the possible use of oxalyl chloride for the preparation of alkyl chlorides and also to compare i t with reagents more commonly used for this purpose, e.g., thionyl chloride and phosgene, a number of alkyl chloroglyoxalates (111) have been prepared and studied with respect to their decomposition behavior. The structural parallelism among the alkyl chlorosulfinates I, the alkyl chloroformates I1 and the alkyl (1) This research was carried out under grants from the Research Corporation and the Graduate Research Council of the University of Wyoming and is abstracted from the M.S. Thesis of R. E. M., University of Wyoming, August, 1961. (2) Presented in part at the Northwest Regional Meeting of the American Chemical Society, Pullman, Wssh., June, 1962. (31 Research Corporation Fellow, 1960-1961. (4) R. Adams and L H. Ulich. J . A m . Chcm Soc , a,599 (1920). ( 5 ) R . Adams and co-workers, rbid, ST, 2716 (1915); S8, 2514 (1916); 40, 424 (1918), studied the reactions of oxalyl chloride with hydroxylic reagents a6 preparative routes to esters and olefins.
chloroglyoxalates I11 led to the expectation that the last would suffer facile decomposition with the formation of an alkyl chloride, carbon dioxide and carbon monoxide. Moreover, i t was anticipated that the decomposition of 111 would respond, ratewise and stereochemically, to changes in intra- and extramolecular environment in much the same manner as do the structural analogs I and II.6 Finally, on the basis of alkylROSOCl
( Ij
+RCl
+ SOn
0 I1
ROCCl 0 0
/I
I1
ROC-CCl
(11) -+ RC1
(111)+RCl
+ C02
+ Cot + CO
oxygen bond strengths, i t was expected that the alkyl chloroglyoxalates would show a thermal stability inter( 6 ) Summarizing discussions may be found in E. s. Gould, "Mechanism and Structure in Organic Chemistry," Holt-Dryden, New York, N . Y.,19.59, p. 294, and J. Hine, "l'bysical Organic Chemistry," McGraw-Hill Book Co., Inc., h*ew York, N. Y . , 1956, p. 114.
586
SARA JANE
RHOADS AND ROBERT E. MICHEL
Vol. 85
TABLE I DECOMPOSITION OF ALKYL CHLOROGLYOXALATES IN THE PRESENCE OF PYRIDINE 0
0
II II
A
ROC-CC1
__t
RCI
CrHrN Time, hr.
T, O C .
R
GHc n-C& 2--17 PhCHCHa
I
3.0 3.5 6.0 5.5
110 f 10 125 f 10 100 f 10 100 f 10
PhCHCHa
Yield, % (RCI olefin)
+
*.
90 95 96 92
,
Product compositiona RCl
b
Olefin
. . ... .. . . . . . .. . .
c
60 11
GHsCl n-C,HoCI 2-CoHnC1, 8548% PhCHCICHt, 90-95%
a-octene, 12-15% PhCH-CH,, 5 1 0 %
51
PhCHCICHa, 100%
None
60
e
10.0
6gd
I
Gas evolved % theery
+ oletin + CO f C02
0
a By g.1.p.c. analysis. Yield not determined. No attempt was made to trap olefin in this case. Reaction carried out in refluxing carbon tetrachloride. * The progress of the reaction was followed by g.1.p.c. analysis of the reaction mixture; in 10 hours, the reaction was 80% complete.
mediate to those of the chlorosulfinates and the chloroformates?
Results The alkyl chloroglyoxalates I11 are readily prepared by simply combining equimolar quantities of oxalyl chloride and the appropriate alcohol. The reactions proceed rapidly a t room temperature when the alcohol is added dropwise to the stirred oxalyl chloride. Distillation of the reaction mixture affords the alkyl chloroglyoxalate as a middle fraction in yields of 60-70%. In this manner, ethyl (IIIa), n-butyl (IIIb), 2-octyl (IIIc) and a-phenethyl chloroglyoxalate (IIId) have been prepared. The properties of these substances are recorded in the Experimental section. 0 0
ROH
0
0
I II +ROC-CCl II I1 + CIC-CCI
secondary alkyl derivatives IIIc and IIId where concurrent olefin (and hydrogen chloride) formation is appreciable. The low yield and the difficulty encountered in the isolation of the products from the pyridine-induced decomposition of the a-phenethyl compound I I I d are attributed to diversion of the product by dehydrohalogenation and subsequent polymerization. The use of carbon tetrachloride as a solvent (Table I) obviated this trouble. The stereochemical outcome of the pyridine-induced decomposition of the alkyl chloroglyoxalates was determined by the study of I I I c and IIId in active form (Table 11). The alkyl chloroglyoxalates were prepared TABLEI1 PYRIDINE-INDUCED DECOMPOSITION OF ACTIVEALKYLCHLORO-
+ HCI
IIIa, R = GHs b, R = n-C'Ho C, R = CHiCHCdHis
GLYOXALATES
R
I
2-COHl7 PhCHCHa
d, R = CsHkHCH,
I
In order to confirm the predicted decomposition pattern, attention was iirst directed to the behavior of the alkyl chloroglyoxalates when heated in the presence of pyridine. Typical results are summarized in Table I. At bath temperatures of 100-125' the pyridineinduced decompositions of the alkyl chloroglyoxalates take place smoothly with the formation of the expected products. The decompositions were followed by collection of evolved gases. Product analysis and identification were made by gas-liquid partition chromatography (g.1.p.c.) of the isolated products. In each case, the addition of pyridine to the alkyl chloroglyoxalate was marked by the formation of a voluminous white precipitate. This solid, presumably the pyridinium salt of the chloroglyoxalate, slowly disappeared during the course of the reaction. Complete decomposition of the chloroglyoxalates occurred only in the presence of an equivalent amount of pyridine; when catalytic amounts of the base were used, a solid sublimate of pyridine hydrochloride began to appear in the condenser soon after decomposition began. Coincident with the removal of pyridine from the reaction mixture in this manner, the decomposition diminished in rate and finally stopped entirely. This effect was most pronounced in the decomposition of the (7) Such an expectation is based on the assumption that the rate-determining step involves heterolysis of the alkyl-oxygen bond and upon the
0 0
///
//O
