Methylmagnesium carbonate

The checkers employed cyclohexanone purchased from Eastman Organic Chemicals and distilled before use, b.p. 155-157°. The ratio of cyclohexanone to methylmagnesium carbonate is fairly critical a proportion of ketone larger than the ratio 1 8 ketone magnesium salt specified yields a pasty product presumably contaminated with monocarboxylated material. A smaller proportion of ketone lowers the yield. 

An earlier series of experiments established useful synthetic transformations involving carboxylation of ketones and nitroalkanes to yield P-keto acids and a-nitro acids respectively (Scheme 94).362 363 The reagent is methylmagnesium carbonate and the intermediate (130) can be alkylated with concomitant decarboxylation to provide greater versatility. These reactions can also be extended to ketone functions in imidazoline- and oxazolidine-diones (Scheme 95).364,365... 

Methylmagnesium Carbonate—An Improved Nonaqueous Deacidification Agent... 

Methylmagnesium carbonate was prepared by saturating an 8% solution of magnesium methoxide in methanol with carbon dioxide at room temperature (25°C) over 2 hr. The resultant solution was clear and colorless. Portions were diluted 10 1 with various solvents and observed for 24 hr for evidence of precipitation. The methanol solution was evaporated to dryness under vacuum on a steam bath, and a friable, glossy white solid was recovered solubility in a number of solvents was determined at the ratio of 1 g of solid in 50 mL solvent. 

Figure 1. Comparative stability to water of magnesium methoxide and methylmagnesium carbonate in methanol. Left flask magnesium methoxide plus 0.5 mL water. Right flask methylmagnesium carbonate plus 5 mL water.

Methylmagnesium carbonate is reported by Finkbeiner and Stiles to have the formula CH30Mg0C02CH3 XC02 where X may vary with solvent and temperature (10). While this formula is empirically correct, the structure has not been conclusively established and may be more complex than indicated. 

Methylmagnesium carbonate is much more stable to water than magnesium methoxide, as illustrated in Figure 1. The methylmagnesium... 

In the methanol-Freon solvent mixture the methylmagnesium carbonate is only about twice as tolerant to water (as measured by the volume of water necessary to cause precipitation) as magnesium methoxide, but this appears to be sufficient to eliminate most, if not all, of the problems with water sensitivity. The difference in stability is apparently a result of the lower concentration of carbon dioxide in the methanol-Freon mixture since the Freon is a much poorer solvent for carbon dioxide than is methanol. 

The solubility of carbon dioxide in the solvent also affects the rate of reaction in the preparation of methylmagnesium carbonate as shown in Table I. In pure methanol the pH became constant after carbonation for 40 min at room temperature, indicating complete reaction, whereas in the methanol-Freon solvent, the reaction takes about 2 hr. 

If desired, the methylmagnesium carbonate can be recovered as a white, brittle solid by evaporation of the solution under vacuum at temperatures up to 100°C. Unlike magnesium methoxide, which becomes almost completely insoluble on recovery as a solid, methylmagnesium carbonate solid is very soluble in methanol but tends to dissolve faster if the methanol is presaturated with carbon dioxide. The solid form provides a convenient method of storage or shipment of the material, much like instant coffee. 

The papers treated with the methylmagnesium carbonate solution showed no precipitation even when allowed to soak in the solution for several minutes and had no visible deposits when they were dried. The texture of the treated papers was also quite different. The treated papers had a pleasant, natural feel, while those treated with magnesium methoxide felt stiff and harsh. The physical properties of the treated papers, the untreated controls, and the solvent-only treated papers, along with the percent fold retention after accelerated aging for 36 days at 100°C, are shown in Table III. 

Reagents i, Methylmagnesium carbonate-DMF ii, H2-MeOH-10% Pd-BaS04 iii, 37% aq. HCHO-DMSO-piperidine iv, NaOMe-MeOH-(5) v, m-MeOC6H4CH2MgCl-THF-CuI vi, MeOH-conc. HC1. 

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