COMMUNICATIONS TO THE EDITOR
3098
double salt also forms solid solutions. Although the internal structure of Li2S04.H20has been determined,22it is unfortunate that the structure of LiNH4S04 has not. It would be interesting t o see (22) G E Ziegler, Z K v i s l , 89, 456 (1934).
1-01.'70
whether the role of NH4+ ion in LiNHdSOJ is the same as that of the combination T,i+-H?O in Li&Od.H?O. DEPARTMENT OF CHEMISTRY ST. JOHN'S UNIVERSITY BROOKLYN, NEWYORK
COh/lMUNICA'I'IONS T O 'THE EDI'I'OK MECHANISM OF THE REACTION OF NITROMETHANE WITH BASES
Sir: We wish to report a mechanism for the reaction of nitromethane with bases in aqueous solutions which accounts for both the initial reaction t o form the salt of the aci form of nitromethane, and the subsequent slower reaction to form the salt of rnethazonic acid.
+ OH-
CH3NOL 2 CHzSO3-
+ H20 + OH-
CH2S02-
kz
--+ 02NCH2CHNO-
(1)
should be noted that the evaluation of K is not our primary purpose. Rather we wish t o show that known values of K s are entirely consistent with our proposed mechanism. This work supports the Pedersen mechnnisin' for pseudo acid behavior of nitro paraffins and gives good agreement with published data2j8on the ionization constant of nitromethane, K N . This constant is related through the water equilibrium constant KW to our equilibrium constant I< in tlic following way
(2)
We have found that basic solutions containing methazonate io? show verg strong absorption of light a t 2,980 A. while acid solutions show none. IVe have also observed that freshly prepared mixtures of dilute solutions of nitromethane and bases react a t relatively slow rates to form the methazonate ion which we can follow by observing the increasing absorption at 2,980 A. with time. The identification of the absorption peak with the methazonate ion has been made by preparing ammonium methazonate by a well established procedure (3) and establishing the absorption spectra pattern of this material.* Our studies a t 25.6' show t h a t the initial rate of formation of methazonate ion is second order with respect to the initial concentration of nitromethane over the range of @Hfrom 9.5 to 12.5. The order with respect to hydroxide ion concentration is second order at p H 9.5, and decreases asymptotically to almost zero order as we increase the fiH to 12.5. I t should be noted that the p H remains constant during the course of any single experiment. On the assumption t h a t the equilibrium in reaction (1) is established very rapidly relative to the velocity of reaction (2), an expression can be derived for the over-all rate from equations (1) and (2) as shown r = - kzK2X2(OH-)' [l K(OH-)]?
+
where = rate of formation of methazonate ion k2 = specific rate constant for reaction (2) K = equilibrium constant for reaction (1) X = eoncentration of nitroinethane plus aci nitromethane.
r
The kinetic data obtained are in complete agreement with equation ( 3 ) . This relation enables us to estimate K a t higher temperatures than has been heretofore possible, and we will also be able to obtain the AH for reaction (1) o n d the nctivatioo energy fnr reaction (2). It
K = Kx/Kv(1) J. K. Pedersen, Det. Kgl. T'ideriak. Selrirab., .2lofh-.f~'s,I f t d L , 1 2 , 1-16 (1932) (in English). (2) D. Turnbull and S. H. hlaron, THISJ O U R N A L , 65, 212 (1943). (3) W. R. Dunstnn and E . Goulding, J . Ckern. S O C . T y a m . , 2 , 1 2 6 2 (1900).
PHYSICS DIVISION CHARLES M. DREW JAMES R. hIcNasnv RESEARCH DEPARTMENT c.s. N A V A L ORDNANCE TESTSTATION IXYOKERS, CHINALAKE,CALIFORXIA ALVIXS. GORDOS RECEIVED MARCH18, 1954
CARBON DIOXIDE FIXATION IN HEART EXTRACTS BY B-HYDROXYISOVALERYL COENZYME A'
Sir: Previous isotopic studies have indicated that isovaleric acid, an intermediate in leucine metabolism, yields acetoacetate in liver t i ~ s u e .b,6? ~ Carbons ~~~ 1 and 2 furnish "acetate" for the well-recognized acetoacetate condensation, and the carbons of the isopropyl group yield acetoacetate by a carbon clioxide-fixing reaction. The intermediate steps in this metabolic pathway have recently been investigated in heart and liver extracts in this laboratory, and the following series of reactions is proposed to account for the results obtained
---
Isovaleryl Co.4 +Senecioyl CoA7 Scnecioyl CoA f HgO -+ H I I TCoA ATP HI\' COA COz HMG COA H M G CoA -+ Acetoacetate Acetyl CoA
+
+
( 1) (2)
(3) (1)
(1) Supported b y grants from t h e National Science Fonndation and the United States Public Health Service. (2) K. Bloch, J. B i d . Chem., 155, 2 5 5 (1914). (3) hl. J. Coon and S. Gurin, i b i d . , 180, 1189 (1949). (4) I. Zabin and K. Bloch, i b i d . , 186, 117 (1950). (5) h l . J. Coon, ibid., 187, 71 (1950). (6) G. W. E. Plaut and H. A. Lardy, ibid.. 192, 435 (1931). (7) Abbreviations: acyl Coenzyme A derivativ?s, acyl C o A ; P-hydroxyisovaleryl CoA, H I V CoA; P-liydro4y-P-methylglutaryl CoA, HMG CoA; adenosine triphosyhote. A T P ; tris-(hydroxymPthyl)-nwinomPthnne, T r i s .
