4002
J. D.
C H A N L E Y AND EDWARD
outlet to a trap containing a concentrated solution of sodium hydroxide for absorption of gaseous HC1. Charged to the flask were 40.9 g. (0.25 mole) of ethyltrichlorosilane. 48.1 g. (0.25 mole) of ethyltriethoxysilane and 500 ml. od reagent-grade benzene. The reactants were cooled t o 5 in a n ice-bath. 1%-ater (27.0 ml.) was added during 17 minutes at 3.5-11 O , with continuous stirring. The reaction mixture was then heated s l o ~ ~to l y facilitate the removal of hydrogen chloride. During 85 minutes, the boiling point rose from 44 to 68”. A Dran-Stark trap now replaced the addition tube. The aqueous layer wliich was separated also contained ethanol, benzene, and some HC1; total volume, 62.3 ml. The gain in weight of the caustic absorber approached the theoretical value. The solvents w r e distilled (480 ml., b.p. to 86’). The residue (74.4 8.) was filtered from a sinal1 amount of gel and distilled using thc Claisen-type head previously described. Three fractions mere taken: (1) 6.70g., b p. 138-140”, i . O % -0CgHj; (2) 2.6 f . , b.p. 119-161 , i’.lVo. -0CzH.; ( 3 ) 3.7 g., b.p. 161176 , 6.2% -OCnHj. The residue, a stiff, balsam-like material, weighed 26.5 g. and contained 5.3% -0C2IIz Hydrolysis in Ethanol Solution.-One-half mole (96.2 g.) of ethyltriethoxysilane and 500 ml. of absolute ethyl alcohol were charged to the reaction flask. The water (27.0 ml. containing 2.5 ml. of 0.5 N HC1) was added in 12 minutes a t 27-33”. H e a t was applied slomly; then the reaction mixture was maintained a t the boiliu,: point (78”) for 3 hours. A still-head was attached, arid alcohol was distilled until th? liquid temperature reached 93 ’. 1-acuum diitillation fcl-
[ C O N T K I B L T I O S F R O M THE
DBPARTIIENT OF
lowed immediately, giving: 7.5 g., b.p. 143-154” a t 0.; m m . , 30.1yo -OC2H3; 3.5 g., b.p. 166-180” at 0.5 nint., 15.5% -0C2IIa; 34.4 g. residue, 14.0 -0C21-L. Alkaline hydrolysis in ethanol was carried out similarly, the €IC1 being replaced by a n equivalent volume of 0.5 iV sodium hydroxide. There w:is some gel present after the heating period. The mixture was cooled and blown with COz for 1.5 hours to remove alkali. The carbonate formed and the gel present mere removed by filtering through a bed of Dicalite. dfter ethanol was distilled, a second filtration produced 1-3 g. more of gel. The concentrate was \vashrtl several times witli water. On vacuum distillation, o r ~ i yit11 inconsequential yield of liquid was obtained. Thc gelled residue weighed 22 t o 32 g. on several trials. Using less than three molar equivalents of water, however, distillable reaction products were obtained, as described previously.
Acknowledgment.-The distillations involving the spinning-band columns were carried out by E. M. Hadsell and Mrs. Dorothea Ladd. The ultimate analyses and molecular-weight determinations were carried out by various members of the Analytical Chemistry Unit of this Laboratory. C.A. Hirt is responsible for the infrared spectrograms. II’e wish to thank all these individuals for their assistance. SCHENECTADY, S.1’.
CHEhIIS~l’RY, T H E hrOUliT S I N A I HOSPITAL]
The Mechanism of the Hydrolysis of Organic Phosphates. BY J.
VOl. 77
FEAGESON
111. Arcjmatic Phosphates’
1). CHANLEY 4 S D EDWARD FEAGESOX RECEIVED FEDRTJARY 8 , 1955
The rates of the hydrolysis, over the PH range 1-10, of the following six compouuds: phenyl (I), m-carboxyphenyl(I1). p-carboxyphenyl(III), or-iiaphthyl (IV), &naphthyl (17) and 8-carboxy-~~-naphthyl (VI) phosphates have been determined. First-order kinetics were observed in each instance. 411 six compounds exhibited a maximum rate of hydrolysis in an interqtahle at pH of 8 and above. An explanatiori for the obmediate PH range, were quite stable a t pII of I , and cotnplet I group is discussed. The pH vs. hydrolysis rate curve for served PH dependency is offered atid the itifluencc of the carh other compounds, but resembles that of o-carboxy-substicompound VI differs fundaiuentnlly from that observed with tuted aromatic phosphoric acid esters. This observation, iii conjiinctioii tvith other evidence, supports the view that the hydrolysis of compound VI proceeds, in contrad;stinctioll t o compounds I through V,by a “participation” mechanism which involves the attack of the carboxylate anion on the phosphorus with forination of a seven-membered ring “transition state.” The various ionization constants of compounds I through VI have been determined and the entropies and heats of activation evaluated.
In continuation of our studiesPa,I’ on the hydrolysis of aromatic phosphoric esters, we wish to report on the hydrolysis of the following six compounds: phenyl (I), m-carboxyphenyl (11), pcarboxyphenyl (111), a-naphthyl (IV) , P-naphthyl (V) and S-carboxy-a-naphthyl (1-1)phosphate to the parent phenol or naphthol and phosphoric acid. Compounds I, I1 and I11 were chosen for study, since they form-in conjunction with the previously investigated o-carboxyphenyl phosphate (salicyl phosphate)-a series, which lends itself particularly well to a study of the effect exerted on the hydrolysis by the intact carboxyl group and carboxvlate anion. ComDounds IV and V are related to ’ o-carboxynaphth$l phosphates previously studied, while with compound ITI the carboxyl group, albeit in the other ring, is so close to the phosphate grouping as to suggest “a priori” the (1) This work >!as supported i n p a r t b y a g r a n t from the Sational Science Forindation. T h e material K W pre7ented in p a r t a t the A n n u a l Afeeting of the American Chemical Societr 111 Xew York Citv, Division of Organic Chemistrv, on Septenlher Ili, l%L, 1,or t h e prrcedini: papers in this series see reference 2a,h. ( 2 ) (a1 J . D. Chanley, E. M . Gindler and XI. Sobotka, THISJ O I J R X \ I . , 7 4 , 4347 ( 1 9 . 7 2 ~ ; ( h ) J . D. Chanley and E. 11. Gindlrr, i b i d . , 75, 403.5 (1933).
possibility of behavior analogous to the ortho position. RI RI 1 1
OPOBH?
07”;
I
Q\Rl
R? I, K, = H;R* = H IT:, R1 11. R1 = COO€%;R2 = FI Rz 111, R1 = H : RJ = COOH vj Ri R;
=
OPOsHz; H ; Ra = I-I
€1 H OPOsOH; ; RI 1’1, R1 = OPOsH; Ro = 14: Rq = COOH
pH Dependency and Rates.-The rates of hydrolysis of compounds I through VI were determined a t SO” over the pH range 1-10 in buffered medium of ionic strength p = 0.1 by analysis for liberated phosphoric acid. In each instance firstorder kinetics obtained throughout the course of the reaction. -111 six compounds exhibited a maximum rate of hydrolysis in an intermediate FH region, were quite stable a t $H ca. 1, and completely stable a t PH of 8 and above (see Figs. 1
Aug. 5 , 1955
HYDROLYSIS O F AROMATIC PHOSPHATES
4003
0'
I
2
4
3
5
6
PH . Fig. 1 -Observed rates of hydrolysis in hours-' at 80' for compounds I, I V and V a t various PH values are indicated by 0 , @, 0 . respectively The solid curve is the theoretical one.
and 2). The same reasoning as before2avb was employed in the elucidation of the p H dependency for the hydrolysis of these compounds. The rate equation, deduced to describe the observed rate of hydrolysis a t any p H for compounds I, IV and V is
-20
1
2
4
3
5
6
PH. Fig 2.-Logarithms of the observed rates of hydrolysis at 80" for compounds 11, I11 and VI at various PH values are indicated by 0 , 0 and @, respectively. The solid curve is the theoretical one.
Only a t pH 1 do we encounter a significant concentration of un-ionized material; a t this pH, the rate of hydrolysis is substantially accounted for by the monoionic species present. The specific rate constants kl and k 2 were obtained kobsrl = kj.11, (a) in the same manner as previously described.2d+b and for compounds 11,I11 and VI The determination of the various ionization constants (Kl,K2, &) (cf. Table 11) a t ionic strength kobad = k l J f , 4- k J I 2 (b) where in both equations kl is the specific rate con- p = 0.1 makes possible the calculation of the stant for the hydrolysis of the monoionic form, mole fractions (AIl, M 2 , etc.)2asba t any pH. The while M I is the mole fraction of this form a t the specific rate constants k l of the unsubstituted particular pH; k2 (referring only to the carboxy phosphates were computed from the observed rate substituted compounds) is the specific rate con- constants a t PH 3.8. At this pH Ml is ca. 99%. stant associated with the diionic form and M 2the For the carboxy substituted phosphoric acid esters (11, I11 and VI) k, and k2 were evaluated from the mole fraction of this form a t the particular pH. observed rate constants a t p H 2.3 and 4.S. The Iosrc SPECIES observed rates of hydrolysis a t a number of other pH's then were compared with the values calculated yo Po Po from equations a and b (cf. Table I, Figs. 1 and 2). R-0-P-OH R-0-P-OH R-O-P-OThe agreement between observed and calculated \OH \o\0values is very satisfactory. In general the greater Uti-ionized (M0) Lfonoionic (11,) Diionic (>I2) deviations occur a t higher pH's since small changes 12 = phenyl(1). a-naphthyl ( I l r ) , &naphthyl (V) in pH effect a considerable percentage change in the mole fraction of the reactive species. The various specific rate constants are given in Table 11. It should be mentioned a t this point that this agreement was obtained for runs made a t 80", Un-ionized ( A i " ) LIonoiouic ( M I ) whereas the mole fractions were calculated from the p K ' s determined a t 26 1". This is permissible 70 30 if neither the p K ' s nor the PH's of the buffer change substantially with temperature or if the changes in -coo --cor)the pK's with temperature are compensated for by concomitant changes in the p H of the buffer. Diionic (AT?) Triionic ( h l , ) The rates were much too slow to be accurately R = phenyl (11, 111), R = naphthyl ( V I ) /
R-o-pqzFIR-o-pq:I
4004
J. D. CH.~TLEY AND EDWARD FEAGESON
Vol. 7 ;
TABLE I HYDROLYSIS OF COMPOUNDS 1-Wa kobsd.
PH
.'do
1.10 1.31
0.44 .33 ,64
2.37 2.96 R .83 4 90 A 74
01
. .
li.2(ib
,
kcaicd.
MI Mz .\f8 h r . ? X 1000 Phenyl phosphate (I) 0.56 ,. 52.3 65.1 .li7 ._ 66.5 78.3 ,9G .. 111 111 .99 ,. 115 11.5 .!>&I 0 01 113 ill.:) .81 09 1 I!: 10.5 ..i8 .4? ($82 tj74 ,211 .i1 31.1 :i4 2
M n
kobad.
keelcd.
.111 J f 2 h r . - l X 1000 a - X a p h t h y l phosphate (IV)
OH
0.43
0.6i
, .
26.3
".ti
0 5rr
0 41
..
..
.,
...
...
..
..
.0.5 .IO
.95
48.3 .>1.4
49 8 ,?lt'
.12
.88
.,
..
. w .x
.
.!IO .!IC1
0.01
no
..
.!IS
.iJi
91 .GO
Xi',
III
.
..
,
..
..
..
.. ..
..i2
,47
.
.18 .li:3
,
,
.
..
...
0 . 0 1 218 .i7 , 1 5 1 0 7 t;!1 28107 ,
..?I;
1;
koalcd.
68 , 5 ... 13t
IiiJ.
3
...
1XL I43 14,; (1.*5, 13:i 1:i-I .1 87 (1 14-I
001 .09 I!) .W
.:+I
i
i!i!l
,.
227 (107) 110
.
.
fi4
1g.O
J:
