Formation Of Dimethyl Sulfide Research Articles

Preparation and Properties of Trimethylsulfonium-Tetrahydrofolate Methyltransferase

Abstract An enzyme that catalyzes the transfer of a methyl group from trimethylsulfonium chloride to tetrahydrofolate has been isolated from a species of Pseudomonas. This enzyme has been partially purified and several of its properties have been studied. The reaction can be formulated as a simple methyl transfer, with the formation of dimethyl sulfide and 5-methyltetrahydrofolate. Neither S-adenosylmethionine nor dimethyl-β-propiothetin can replace trimethylsulfonium chloride as methyl donor. 2-Mercaptoethanol is unable to replace tetrahydrofolate as methyl acceptor. The enzyme has a molecular weight of approximately 100,000. There is no vitamin B12 derivative associated with the enzyme.

Chemical Equilibria and Kinetics in the Catalytic Formation of Methyl Mercaptan and Dimethyl Sulfide

The relation between methyl mercaptan and dimethyl sulfide, two product com-pon entsobtained from the vapor phase reaction of hydrogen sulfide and methyl alcohol over gamma-alumina catalyst, agreed with the equilibrium calculated from the equation 2 CH3SH CHCH3SCHCH3+HCH2S, assuming that Kp is 1.57 at 370°C. The true equilibrium states were confirmed by carrying out the reaction from both sides of the equation. A 2.2 kcal difference was noted in the value of free energy of formation of the reaction between the value calculated from the measured equilibria and that reported in the literature. This may be attributed to the probable errors in estimating the heat of formation of methyl mercaptan and dimethyl sulfide. The velocity of formation of methyl mercaptan and dimethyl sulfide from hydrogen sulfide and methyl alcohol over gamma-alumina catalyst of 2 mm diameter at 390°C was shown as follows:

Synthesis of Methyl Mercaptan and Dimethyl Sulfide

Vapor phase reaction of hydrogen sulfide with methyl alcohol over gamma-alumina to form methyl mercaptan and dimethyl sulfide was studied at 330, 370, 410, and 450°C; under pressures of 1, 4, and 5 kg/cm2; and in the mole ratios of hydrogen sulfide to methyl alcohol of 1 and 5. When the reaction was conducted above 400°C, formation of a small amount of permanent gases was observed. Below 400°C, however, the product consisted practi-cally of dimethyl ether, methyl mercaptan, dimethyl sulfide, and water. As the contact time was Prolonged, the amount of product dimethyl ether reached its maximum and then raduallv decreased to zero. Methyl mercaptan and dimethyl sulfide seemed to be formed simultaneously on the catalyst surface. The apparent activation energies were 10 kcal/mol as calculated based on the reaction rate of methyl alcohol, and 25 kcal/mol as cal-culated based on the rate of formation of methyl mercaptan and dimethyl sulfide.