Kinetic acetonation

The kinetic-acetonation procedure previously reported,107 employing alkyl isopropenyl ethers in N,N-dimethylformamide, and applied to the common pentoses and hexoses, has been extended to various hexuloses, oligosaccharides, and other sugar systems.108 Maltose gave the 4, 6 -monoacetal, isolated as the crystalline hexaacetate, on treatment with isopropenyl methyl ether inN,N-dimethylformamide in the presence of p-toluenesulfonic acid. 

Gelas and D. Horton, Kinetic acetonation of D-mannose preparation of 4,6-mono and 2,3 4,6-di-0-isopropylidene-D-mannose, Carbohydr. Res. 67 371 (1978). 

E. Fanton, J. Gelas, D. Horton, K. Karl, R. Khan, C. Knan Lee, and G. Paid, Kinetic acetonation of sucrose preparative access to a cbirally substituted 1,3,6-lrioxacyclooctane system, J. Org. Chem 46 4057 (1981). 

Secondary hydroxyl groups also react if sufficient amount of rm-butylchlorodi-phenylsilane — imidazole — DMF reagent is used. The less hindered OH-2 of 1,4-anhydro-5,6-0-isopropylidene-D-glucitol was silylated in more than 78% yield [447]. Of the two secondary hydroxyl groups of the 4, 6 -0-isopropylidene-a-D-glucopyra-nosyl part of a kinetic acetonation product of maltose, that one at C-3 was selectively protected [448]. 

J. Gelas and D. Horton, Kinetic acetonation of o-galactose, D-allose and ivtalose with alkyl propenyl ethers as a preparative route to the 4,6-(7-isopropylidene aldohexopyranoses, Car-bohydr. Res. 77 103 (1979). 

Kinetic acetonation (2) of D-ribose (1) to give 3/4-0-isopropylidene-D-ribopyranose (16), followed by the direct Wittig reaction gave mainly (85%) the product 17 In contrast, the thermodynamic acetonation product, 2,3-Q-isopropylidene-D-ribofuranose (18) afforded mainly (-70%) the Z (cis) ester, isolated as its 6,7-diacetate 19 ... 

The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

The following data were collected during a kinetic study of the iodination of acetone by measuring the concentration of unreacted I2 in solution. ... 

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

Ma.nufa.cture. Mesityl oxide is produced by the Hquid-phase dehydration of diacetone alcohol ia the presence of acidic catalysts at 100—120°C and atmospheric pressure. As a precursor to MIBK, mesityl oxide is prepared ia this manner ia a distillation column ia which acetone is removed overhead and water-saturated mesityl oxide is produced from a side-draw. Suitable catalysts are phosphoric acid (177,178) and sulfuric acid (179,180). The kinetics of the reaction over phosphoric acid have been reported (181). 

Hydrolysis to Glycols. Ethylene chlorohydrin and propylene chlorohydrin may be hydrolyzed ia the presence of such bases as alkaU metal bicarbonates sodium hydroxide, and sodium carbonate (31—33). In water at 97°C, l-chloro-2-propanol forms acid, acetone, and propylene glycol [57-55-6] simultaneously the kinetics of production are first order ia each case, and the specific rate constants are nearly equal. The relative rates of solvolysis of... 

Kelkar and McCarthy (1995) proposed another method to use the feedforward experiments to develop a kinetic model in a CSTR. An initial experimental design is augmented in a stepwise manner with additional experiments until a satisfactory model is developed. For augmenting data, experiments are selected in a way to increase the determinant of the correlation matrix. The method is demonstrated on kinetic model development for the aldol condensation of acetone over a mixed oxide catalyst. 

The dehydration reactions have somewhat higher activation energies than the addition step and are not usually observed under strictly controlled kinetic conditions. Detailed kinetic studies have provided rate and equilibrium constants for the individual steps in some cases. The results for the acetone-benzaldehyde system in the presence of hydroxide ion are given below. Note that is sufficiently large to drive the first equilibrium forward. 

Kinetic evidence in the hydroxide-catalyzed halogenation of acetone provides definitive mechanistic information. The overall reaction is... 

The rate equation is first-order in acetone, first-order in hydroxide, but it is independent of (i.e., zero order in) the halogen X2. Moreover, the rate is the same whether X2 is chlorine, bromine, or iodine. These results can only mean that the transition state of the rds contains the elements of acetone and hydroxide, but not of the halogen, which must enter the product in a fast reaction following the rds. Scheme VI satisfies these kinetic requirements. 

In confirmation, when acetone-dg was studied, a very substantial kinetic isotope effect was observed, being about 7 to 12 depending upon the base catalyst. 

If (A i[X ]/A 2[Y ]) is not much smaller than unity, then as the substitution reaction proceeds, the increase in [X ] will increase the denominator of Eq. (8-65), slowing the reaction and causing deviation from simple first-order kinetics. This mass-law or common-ion effect is characteristic of an S l process, although, as already seen, it is not a necessary condition. The common-ion effect (also called external return) occurs only with the common ion and must be distinguished from a general kinetic salt effect, which will operate with any ion. An example is provided by the hydrolysis of triphenylmethyl chloride (trityl chloride) the addition of 0.01 M NaCl decreased the rate by fourfold. The solvolysis rate of diphenylmethyl chloride in 80% aqueous acetone was decreased by LiCl but increased by LiBr. ° The 5 2 mechanism will also yield first-order kinetics in a solvolysis reaction, but it should not be susceptible to a common-ion rate inhibition. 

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Thorium oxide on activated carbon was prepared by absorption of thorium nitrate from its solution in anhydrous acetone on the activated carbon Supersorbon. The excess solution was decanted, the catalyst was dried at 80 °C, and the adsorbed thorium oxide was decomposed by excess 5% ammonium hydroxide solution. After repeated washing and decanta-nation with distilled water and acetone, the catalyst was dried at 180°C. It was then stabilized by heating to 360°C for 5 hr in a stream of nitrogen. The content of thorium oxide was 2.9% (wt.). The BET surface area was 870 m2/g. Prior to kinetic measurements, the catalyst was modified by passing over acetic acid vapors (100 g acid/1 g catalyst). 

There have been relatively few detailed kinetic studies of the decompositions of metal acetates, which usually react to yield [1046] either metal oxide and acetone or metal and acetic acid (+C02 + H2 + C). Copper(II) acetate resembles the formate in producing a volatile intermediate [copper(I) acetate] [152,1046,1047]. 

The first extensive kinetic study of these reactions was carried out by Ingold et a/.7I3b, who demonstrated that for the two-alkyl exchange reaction, i.e. the reverse direction of equilibrium (283), the kinetics in acetone and ethanol were cleanly second-order, viz. 

Zeroth-order kinetics. The rate of bromination of acetone in acidic aqueous solution is governed by the enolization step. With [(CH3>2CO]o s> [B lo, the reaction rate is... 

Another example of an enzymatic one-pot multiple Diels-Alder reaction is illustrated in Table 4.20 [83]. Racemic furfuryl alcohols 130 in the presence of ethoxy vinyl methyl fumarate 131 and enzyme TOYOBO-LIP undergo enzymatic acylation followed by kinetic enzymatic resolution to give the acyl derivatives 132 which then affords the adducts 133 and 134 by intramolecular Diels-Alder reaction 3-methyl-furfuryl alcohol 130 (R = Me) in acetone gives the best results. 

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