DIETHYLACYLOXYETIIYLPI-IOSPI-IONATES
Dec. 5, 1956
GO25
ORGANIC AND BIOLOGICAL CHEMISTRY [CONTRIBUTION FROM
THE
FATTY ACIDPRODUCERS' COUNCIL OF THE ASSOCIATION OF AMERICAN SOAPAND GLYCERINE PRODUCERS, INC., AND THE EASTERN REGIONAL RESEARCH LABORATORY]
'
Phosphorus Derivatives of Fatty Acids. 11. Diethyl Acyloxyethylphosphonates2 BY BERNARD L ~ C K E R M A NT. , ~ A.
JORDAN3 AND
DANIELS W E R N
RECEIVED JUNE 18, 1956 Diethyl acyloxyethylphosphonates derived from acetic, caproic, lauric, myristic, palmitic, stearic and oleic acids were prepared by the reaction of the 2-bromoethyl esters with triethyl phosphite. Various physical properties of these compounds are reported. The free phosphonic acids could not be obtained from the esters by the usual means; hydrolysis even under the mildest acidic conditions liberated the parent fatty acid. A more detailed study of the hydrolysis led to the following conclusions: (1) hydrolysis of the carboxyl ester occurs much more rapidly than that of the phosphonic esters, (2) rate of hydrolysis is not affected by length of acyl chain or size of phosphonic ester groups, and (3) rate of hydrolysis is approximately the same as that of the ethyl ester of the corresponding fatty acid.
uct obtainable was the parent fatty acid. This In the first paper of this ~ e r i e s ,alkylphos~ phonates were shown to be much more resistant to unexpected result prompted a more detailed study hydrolysis than acylphosphonates of the same mo- of the hydrolysis of these compounds under acid lecular weight. Diethyl lauroxyethylphosphonate, conditions. C H ~ ( C H ~ ) & O O C H ~ C H ~ P ( O ) ( O C H ~ C was H ~ ) ~ , The study of the rate and extent of hydrolysis used in the hydrolysis experiments as an example included ethyl laurate and diethyl myristoylphosof an alkylphosphonate derived from a fatty acid. phonate in addition to alkylphosphonates of various Because of the greater stability of this type of molecular weights. The samples were hydrolyzed compound, i t was thought that a study of the in 2075 aqueous-acetone solution which was 0.1 N acyloxyethylphosphonates would be of practical with respect to hydrochloric acid. T o compensate and theoretical interest. An examination of the for differences in molecular weight of the samples literature revealed no examples of this specific type the results were calculated on the basis of equivalents of acid produced per mole. The reof phosphorus derivative. This paper describes the preparation and prop- sults are shown in Fig. 1. erties of diethyl acyloxyethylphosphonates deI I I I rived from acetic, caproic, lauric, myristic, palmitic, stearic and oleic acids. The diethyl esters were chosen in order to achieve structural consistency with the compounds described previously. In addition, di-n-butyl and di-n-hexyl lauroxyethylphosphonate were prepared for the purpose of comparison. The dialkyl acyloxyethylphosphonates were prepared by heating the 2-bromoethyl ester of the appropriate fatty acid with an excess of the trialkyl DIALKY L ACY LOXY E T H Y LPHOSPHONAT E! phosphite a t elevated temperature for several hours. After the unused trialkyl phosphite was removed, the residue was distilled under high vacETHYL LAURATE uum with the desired product being obtained in a yield varying from 53 to 85%. The phosphonates derived from acetic, caproic, lauric and oleic acids are colorless liquids a t room temperature while those from m y r i ~ t i c palmitic5 ,~ 0 25 50 75 too 125 and stearic acids are white crystalline solids. PhysiT I M E , HOURS. cal properties of these compounds are listed in Table I. Fig. 1.-Rates of hydrolysis of diethyl myristoylphosThe relative hydrolytic stability of the diethyl phonate, dialkyl acyloxyethylphosphonates and ethyl acyloxyethylphosphonates previously noted4 was laurate a t 61' in aqueous acetone 0.1 N with respect to the basis for attempts to obtain the free phosphonic HCl. acid by acidic hydrolysis. However, even under There was little difference in the rates of hymildly acidic conditions, the only crystalline prod- drolysis of the various dialkyl acyloxyethylphos(1) A laboratory of the Eastern Utilization Research Branch, Agriphonates. A single curve representing five series of cultural Research Service, U. S. Department of Agriculture. closely coinciding points was drawn for these com(2) Presented in part at the Fall Meeting of t h e American Chemical pounds. Variation in the acyl chain length inSociety, Atlantic City, New Jersey, September 16-21, 1958. (3) Fellow of t h e F a t t y Acid Producers' Council of t h e Ascluded the Ce, Clz and CIScompounds. The ethyl, sociation of American Soap a n d Glycerine Producers, Inc. n-butyl and n-hexyl groups comprised the varia(4) B. Ackerman. T.A. Jordan, C. R. E d d y a n d D. Swern, THIS tion in the phosphonic esters. Neither of these JOURNAL, 78, 4444 (1956). variations had any appreciable effect on the rate of ( 5 ) Diethyl myristoxy- a n d palmitoxyethylphosphonate were very slow to crystallize a t room temperature. hydrolysis. The extent of hydrolysis increased D
1
TABLE I CIIAKAC.TSKIZAI.IUN OI? DIALKYL '~\CYI,UXY~.TIIYLP~IUSPI-IONA.TES,l ~ , C O O C H ~ C H z ~ ( 0 ) ( O K 2 ) 2 .if. 1,. ,
K1C00( 1 1 8 = ethyl)
O C
.
Acetosy ... Caproiisy ... Lauroxy a-21 Myristuxy 31-31" Paltnitoxy 10-41 Steciroxy .Hj Oleosy ... Dj-n-butyl l a u r o x q . e l l l y l ~ l ~ u s ~ ~ l i o i ~.u.t.c Iji-n-licsyl l a u r o s y e t h y l p l ~ o s l ~ l i ~ i i .~ t.~
"C
B.p. him.
162 20.0 103-105 0.1 104 .2 257-150 .I 109-172 .1 155-191 .1 184 .1 164-172 .1 193--197 ,1
reldtively rapidly LO J J O U L oiic ccluil .tlerit cd acid produced, and only slowly afterward, iiidicatiiig that one of the three possible linkages was being preferentially attacked. The parent fatty acid was isolated and identified from the residual solutions; thus it is apparent that hydrolysis proceeded for the most part a t the carboxylic ester. On the other hand it is unlikely that the hydrolysis curve for the acyloxyethylphosphonates from 0 to 30 hours represents only the cleavage of the carboxylic ester. It is probable that some small amount of phosphonic ester is hydrolyzed before hydrolysis of the carboxylic ester is complete. This would account for the deviation of the acyloxyethylphosphonate curve from that of ethyl laurate. If the contribution made by the phosphonic ester groups is taken into account, the two curves would coincide more closely. This indicates that the presence of the phosphonate group has little or no effect on the hydrolytic stability of the carboxylic ester. In contrast to tlie acyloxyethylphosphonates, diethyl acylphosphonates hydrolyze to give three equivalents of acid per mole in neutral solution, as reported p r c v i ~ u s l yand , ~ under the present conditions. It is likely that the hydrolysis of acylphosphonates in mild acid solution proceeds in the same order as in neutral solution, L e . , the acyl carbon-phosphorus bond is cleaved first. The resulting fragment, HPO(OCH&!H&, is therefore much less stable to further hydrolysis than the fragiiieiit HOCHnCH2PO(OCH$2H3)2 which is obtained initially from the hydrolysis of the diethyl acyloxyethylphosphonates. The greater stability of the latter is clue to the presence of the alkyl c:trbon-pliosphorus bond. Infrared spectra were obtained on tlic diethyl acyloxyethylphosphonates having 2 , 12 and 1s carbon atoms in the acyl groups, and also on diethyl oleoxyethylphosphonate. A spectrum for diethyl laurosyethylphosphonatc is typical.* The absorption bands which may be associated with the phosphorus-containing part of the molecule are a t positions similar to those of the diethyl acylphosphonates,* as shown in Table 11. I n this table, the ( 6 ) This spectrum has been deposited a s Document No. 4977 with the American Documentation Institute Auxiliary Publications Project, PhotodupllLdtion Serpice, Library of Congress, Washington 25, D C Either a photoprint or a 35-mm microfilm copy m a y be secured for $1 'i 1 ~ iblc ) in dd\ u i ( c tiy rheih ur money order payable t o Chief t ' l i r ~ t ~ ~ i l i r ~ , l i ~ . ~5t1i 1~ \~ 1 ~ ~( c
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