From the points taken between about 0.1 and 0.3 sec, k values of 2.10 ± 0.10, 1.69 ± 0.14, and 1.49 ± 0.12 sec-1 were obtained from the three sets of runs. These values were taken as first-order rate constants for hydrolysis at pH's 6.56 ± 0.18,6.69 ± 0.17, and 6.85 ± 0.20, respectively.Kinetics of Imine Hydrolysis. The kinetics of hydrolysis of the N-isobutylidenemethylamine were studied at (5) All the ± values listed are standard deviations.

Stopped-flow spectrophotometric measurements on the reaction of isobutyraldehyde with methylamine in water at 35°over the pH range 10.1-11.5 gave a value of 8.5 ± 0.5 M-1 for the equilibrium constant for addition of the amine to the aldehyde, and a value of 6.2 ± 0.7 sec-1 for kc, the rate constant for dehydration of the carbinolamine to N-isobutylidenemethylamine. Kinetic studies of methylammonium chloride catalysis of the oximation of isobutyraldehyde at pH 8.5-9.8 gave values of kcKc* in agreement with the stopped-flow measurement, but at pH 7.6 larger values were obtained, suggesting acid catalysis of the dehydration of the carbinolamine. The equilibrium constant for the addition of hydroxylamine to isobutyraldehyde was found to be 105 ± 11 M~\ and the rate constant for dehydration of the adduct to give oxime fit the equation kd = (6.5 X 105[H+] + 3.2 X 10~12/ [H+] + 4.6 X 10-3) sec-1. A kinetic study of the hydration of isobutyraldehyde in the presence of N-methylmorpholine buffers showed that the reaction was fast enough that the hydration-dehydration equilibrium could be treated as continually established throughout the studies of the reaction of isobutyraldehyde. Structural effects on equilibrium constants for addition to isobutyraldehyde are discussed.

A. Materials. Pyridine was Eastman grade, used without further purification. Rose Bengal (Eastman grade, C.I. 45440, 84% dye content) was purified by dissolving 2 g in the minimum amount of 0.14 M NH4OH, and passing this over a 2 X 20 in. bed of Sephadex G-25 Fine (Pharmacia Fine Chemicals, Inc.) using water as eluent. Several bands were obtained, the main one being collected and acidified with dilute HC1, and the Rose Bengal free acid collected by filtration. After drying, a 1.14 X 10~4 M solution in pyridine had a Xmal at 573 nm with D573 1.13, ¿>546 0.35, both for 1-mm layers. The dye does not follow Beer's law, the Omax shifting hypso-and hyperchromically upon dilution. 2-Methyl-2pentene was Phillips Petroleum Company pure grade, 99 mol % minimum. This was passed over a short column of aluminum oxide (Woelm Neutral) prior to use. Triethylamine was Eastman grade, once distilled.B. Measurements. The reactions were followed by measuring the rate of oxygen consumption in a constant pressure, automatic recording gasometer apparatus. This apparatus is basically a hybrid of two that are described in the literature.18•17 The absorption cell was similar to the one described by Mahoney, et al.,w and the physical arrangement of the gasometer itself was similar to that of Traylor and Russell.17 Pressure differentials were detected by a Schaevitz P476-A10 pressure transducer (0-10 in. of water), which was attached to the gasometer via small-diameter, stainless steel tubing with Swagelok fittings (Teflon front ferrules). The signal from the transducer activated a Harvard infusion-withdrawal pump. This pumped mercury into a gas buret attached to the gasometer until the null point of the transducer was reached. The pump displacement was converted to a voltage change by appropriate gearing of the pump to a Helipot linear potentiometer. Output from the potentiometer was fed into a 10-mV span strip chart recorder, equipped with chart speeds of 2, 5, 8, and 20 in ./hr (Varían Associates Model Gil A). Rates as low as 10-7 M sec-1 can be measured on a 10-ml sample.

and C, and stopcock E was closed. Dried solvent was distilled into A which contained Linde Molecular Sieve 3A Vis-The solvent was then degassed by the freeze-thaw technique. After opening stopcock E, solvent was distilled into B, the stopcock was closed, and the apparatus was removed from the vacuum line at G. The capillary was then crushed by the magnet F, after which the solution was poured from B into C, and shaken well to dissolve the 1. The volume was measured and the cell was placed in the spectrophotometer for absorbance measurements at 546 nm. Kinetic measurements were made with both nitromethane and acetonitrile as solvent. Acetonitrile itself reacts very slowly with 1, whereas nitromethane solutions are stable indefinitely.

Hine and Viaa Hewlett-Packard Model 5750 apparatus fitted with dual thermal conductivlty and hydrogen flame detectors; (b) 150 ft X 0.02 in. stainless steel capillary column lined with DC-550 oil at 110 OC; (c) 50 ft X 0.02 In. capillary suppoct coated opan tubular (SCOT) column lined with Carbowax 20M mounted In a Perkin-Elmer Mark II flame ionization gas chromatograph. (10) Amberlyst-15 resin and literature describing it were obtained from Rohm and Haas Co. This reagent shows considerable promise in effecting acldcatalyzed conversions. (1 1) A NesterIFaust (NFA-100) autoannular spinning band column was used. (12) W. M. Harms and E. J. Elsenbraun, Org. Prep. proced. Int., 4, 67 (1972). (13) Mass spectra were obtained with a Consolldated Electrodynamics Corp. Model 21-1 106 high-resolution mass spectrometer operated under lowresolution conditions at 70 eV. NMR spectra were obtained with a Varian Associates HR-60 or HR-100 spectrometer. Peak positions are reportedIn terms of 6 (pPM) downfield from internal standard tetramethylsilane (6 0). IR spectra were obtalned with a Beckman IR-5A spectrometer as films on NaCl plates or as KBr pellets. Melting points were taken In capillary melting point tubes using a Thomas-Hoover apparatus and are corrected. Boiling points are uncorrected. Cyclohexane used in the reactions was "Baker Analyzed" reagent, spectrophotometric quallty. The benzene used was Fisher Certified reagent (thiophene free). Phillips pure grade isoprene was used in all cycllalkylatlon reactlons. The sulfuric acid used was reagent grade. The petroleum ether, bp 60-68 OC, was redistilled before use. (14) A. A. Khalaf and R. M. Roberts, J. Org. Chem., 34, 3571 (1969). (15) The ketone 14 (Celestollde) was purchased from International Flavors and Fragrances, New York, N.Y. (16) W. Reppe and W. J. Schweckendiek, Justus Liebigs Ann. Chem. 580, 104 (1 948).The reactions of isobutyraldehyde with diamines of the type MeZN(CH2),NH2 where n = 2 , 3 , 4 , and 5 have been studied at various pHs by stopped-flow spectrophotometry. A small amount of aldehyde disappears in an equilibrium process whose rate is too fast to measure. Rough equilibrium constants for this rapid reaction (K,) are determined in the various runs. The K , values at various pHs are resolved into Kca, the equilibrium constant for formation of the carbinolamine i-PrCH(OH)NH(CHZ),NMez, and Kcah, the equilibrium constant for formation of the protonated carbinolamine i-PrCH(OH)NH(CHZ),NHMez+. Also determined in the various runs are the equilibrium constants for a slower reaction ( K 8 ) , in which equilibrium is not established until about 5-50 s. These are resolved into values of Ki,, the equilibrium constants for formation of carbinolamine and imine, and Kith. In all cases Kith covers the formation of protonated carbinolamine and the protonated imine i-PrCH=N(CHZ), NHMeZ+.However, when monoprotonated 2-dimethylaminoethylamine is the reactant much of the product is probably the l,l-dimethyl-2-isopropylimidazolidinium ion, and when monoprotonated 3-dimethyl...