The rate of dimerization of cyclopentadiene and some other cycloaddition reactions is determined by electrophilic solvation of the substrate with some contribution of other solvation factors, primarily nonspecific solvation. The corresponding dependence is described by multiparameter equations.Spontaneous dimerization of cyclopentadiene slows down upon dilution with various solvents; the maximal deceleration (by a factor of 3.5) was observed in strongly polar acetonitrile [1]. However, C1 oster and Pfeil [2] studied the rate of cyclopentadiene dimerization in 16 solvents and found no clear relation betweem the secondorder rate constant k and such solvent parameters as dielectric constant e, dipole moment m, Hildebrand solubility parameter d, and Reichardt electrophilicity parameter E T [3]. A certain relation (with a number of exceptions) was revealed between log k values and enthalpies of vaporization of the solvents: reduction of the latter parameter by a factor of 2 in going from 1-butanol to diethyl ether leads to decrease in k to a comparable extent. The authors concluded that, in the general case, solvent effect on a dissolved substance cannot be described using a single parameter owing to specific interactions.On the other hand, it is known that interactions of a solute with the solvent can be generalized on the basis of the linear Gibbs energy relationship principle by summation of effects produced by various solvation processes via multiparameter equations [4]. Among the latter, one of the most effective is the extended Koppel'3Pal'm equation which takes into account not only specific and nonspecific solvation but also structural features of the medium [5]. In the present work we made an attempt to generalize the data given in [2] on the rate constants for dimerization of cyclopentadiene at 40oC in 0.6 M solutions using Eq. (1): log k = a 0 + a 1 777 + a 2 777 n 2 3 1 n 2 + 2 e 3 1 2e + 1 + a 3 B + a 4 E T + a 5 d 2 + a 6 V M .(1)Here, n and e are, respectively, the refractive index and dielectric constant which determine solvent polarizability and polarity (i.e., factors responsible for nonspecific solvation); B is the basicity according to Pal'm [4], and E T is the Reichardt electrophilicity parameter [3] (these quantities characterize solvent ability for acid3base interactions, i.e., specific solvation); d is the Hildebrand solubility parameter (its squared value is proportional to the cohesion energy density); and V M is the molar volume which takes into account possible effect of structural factors. The solvent parameters were taken from [4] and reviews [6,7], and the calculation procedure conformed to the IUPAC recommendations concerning the application of correlation analysis in chemistry [8]. The corresponding data are collected in Table 1.However, processing of the data for 17 solvents according to Eq. (1) resulted in a too low [8] multiple correlation coefficient (R = 0.925). However, to reach an acceptable correlation quality, it was sufficient to exclude the most deviating data for only one s...
The process of diene cyclization of 2,3-dimethylbutadiene with allyl methacrylicate was investigated. Effects of temperature, reaction duration, and ratio of reagents on the yield of 1,3,4-trimethylcyclohex-3-en-1-carboxylic acid allyl ester was studied. Optimal conditions of passing the process were found.Esters of alkyl-substutited cyclohexenecarboxylic acids are valuable raw material for the synthesis of a number of compounds including medical preparations, some of which inhibit cholesterin biosynthesis and noticeably reduce its level in blood [1]. Furthermore esters of alkylsubstutited cyclohexenecarboxylic acids are used for the synthesis of tertiary alcohols applied in perfumery compositions [2]. Owing to the dielectric anisotropy, esters are used as components of liquid-crystal compositions for electro-optical instruments. They are also widely applied as softening modifi ers of epoxy resins. Multifunctional monomers of various structures with a certain complex physicochemical characteristics are obtained on the basis of esters of alkyl-substutited cyclohexenecarboxylic acids [3].In the literature there are data on the cyclization of some dienes with acrylates. Ethyl ester of 3,4-dimethylcyclohex-3-en-1-carboxylic acid is obtained by the reaction of 2,3-dimethylbutadiene (DMB) with ethyl acrylate by the Diels-Alder reaction [2]. Methyl ester of 2-methylcyclohex-3-en-1-carboxylic acid is obtained by the condensation of piperylene with methyl acrylate, using equimolar amounts of piperylene and methyl acrylate. The mixture is stirred, put in an autoclave, and heated up for 6 h at 200°С in the presence of hydroquinone. The yield of the ester is 65% [1]. Methyl ester of 1,3,4-trimethylcyclohex-3-en-1-carboxylic acid is obtained by the cyclization of DMB with methyl metacrylate, using a solution of methyl metacrylate and DMB in toluene. The mixture is stirred, put in a glass ampoule, and heated up within 12 h at 140°С in the presence of pyrogallol. The yield of the ester is 70% [3]. No published information on the procedures of preparation of 1,3,4-trimethylcyclohex-3-en-1-carboxylic acid allyl esters (TMCHC AE) is available.The aim of this work was the extension of the assortment of esters of cyclohexenecarboxylic acids due to obtaining new monomers, unsaturated esters of alkylsubstutited cyclohexenecarboxylic acids.To prepare TMCHC AE, we have chosen its synthesis from DMB with methacrylic acid allyl ester (MA AE) has been selected. EXPERIMENTALIn the work we have studied the process of TMCHC AE preparation by DMB diene cyclization with MA AE according to the reaction according to the scheme To obtain TMCHC AE, we used DMB synthesized by a catalytic dehydration of 2,3-dimethyl-2,3-butanediol [4, 5] and chemically-pure grade MA AE.Reaction products were analyzed on a "Chrom-5" chromatograph with a DTP thermal conduction detector and a chromatograph column of 1 m in length and diam-
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