The Rate of Saponification of Some Alkyl rn- and p

The rates of saponification decrease as the size of thc alkyl groups methyl, ethyl and propyl benzoatcs have been mcasurcd. in the amino group increas...
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CHARLESC. PRICEAND WILLIAMJ. BELANCER

2682

converted into a complex like I11 may be inorc reactive because of inductive electron release through the boron atoin to the ring carbon. The efficiency

[COSTRIBUTION FROM

THE

Vol. 76

of sodium fluoride is undoubtedly related to the

great stability of the fluoboratc anion. DURHAM, NEW

HAMPSHIRE

DEPARTMENT OF CIXEXISTRY, UNIVERSITY OF NOTREDAME I

The Rate of Saponification of Some Alkyl rn- and p-Dialkylaminobenzoates BY CHARLES C. PRICE AND WILLIAM J. BELANGER' RECEIVED JANUARY 14, 1964 The influence of m- and p-dimethylamino, diethylamino and di-n-propylamino groups 011 the rates of saponification of methyl, ethyl and propyl benzoatcs have been mcasurcd. The rates of saponification decrease as the size of thc alkyl groups in the amino group increases.

I t has been reported by Price and Lincoln' that and especially m-,t-butylbenzoatcs saponify in 60% acetone a t rates considerably slower than the toluates. I t was suggested that one of the factors responsible was a decrease in the solvation stabilization of the ionic intermediate in saponification due to the bulk of the t-butyl group, as compared to the methyl group.

!I-,

~ ' R O P E R I I E SOP

Isomer

Aleta Pura MCtlL

Para illCt1L

Para

R

CHI CHs CzHb CzH 5 Allyl Allyl

TABLE I S , N - ~ > I A I , K Y L A M I N O AI ~ C I~U~SN Z ~ I C Presn. c

I e

M.P., "C.

I.it. mp., 'C.

150-1 51 233-236, 89-90 191-193 91 126-126.5

l5l* 234-240d 9oe 188-1 (3.Y 9o' 127'

iWetu Para

It was the purpose of the work reported herein to study this effect by changing the size of R, making it dimethylamino, diethylamino and dipropylamino with R' methyl, ethyl or propyl.

-

Experimental3 The properties of the acids used and references to the methods of their preparation are given in Table I. The esters of the aminoacids were prepared by refluxing the acid with alcoholic hydrogen chloride. The esters were fractionally distilled through a 90 X 1.2-cm. glass-spiral column. The properties of othcr esters used are summarized in Tablc 111. Saponification rate measurements in GOY0 acetone* were unsatisfactory because some of the aminoesters saponified so slowly that the acetone turned deep yellow, obscuring the end-point. Solvents that proved satisfactory were 800/0 methanol for the methyl esters, 80% ethanol for the ethyl esters and 80% 1-propanol for the n-propyl esters. The procedure was essentially the same as that described previously2 and the results are summarized in Tables IV. V and 1.1. Some rates of saponification in 6OY0 acetone are summarized in Table V I I . The reaction constants, p . used for calculating the substituent constants, a, in Tables IV, V and VI are given in each table and were estimated from the rates of saponification of the benzoate and toluate esters by the equation l o g ( k n / k ~ )=

UP

'l'iic values assigned to u are indicated in the table.

Discussion Froni the data in Tables IV, V arid VI it can be seen that the rates of saponification of analogous esters with dimethylamino, diethylamino and dipropylamino substituents decrease in the order indi(1) Socony-Vacuum Fellow, 1949-1951. Abstracted from t h e Ph.D. dissertation submitted b y W. J. B . , August. 1951. (2) C . C Price a n d D C. I,incoln, '['HIS J O U R N A L , 73,5838 (1951) ( 3 ) All melting points are corrected. Rlirro:inalyses 1 ) blicrc>~ Tech Lalmral ories, Skokie, Illin