Dimethoxymethane

Dimethoxymethane, also called methylal, is a colorless flammable liquid with a low boiling point, low viscosity and excellent dissolving power. It has a chloroform-like odor and a pungent taste. It is the dimethyl acetal of formaldehyde. Dimethoxymethane is soluble in three parts waterTemplate:Cln and miscible with most common organic solvents.

Synthesis and structure

It can be manufactured by oxidation of methanol or by the reaction of formaldehyde with methanol. In aqueous acid, it is hydrolyzed back to formaldehyde and methanol.

Due to the anomeric effect, dimethoxymethane has a preference toward the gauche conformation with respect to each of the C–O bonds, instead of the anti conformation. Since there are two C–O bonds, the most stable conformation is gauche-gauche, which is around 7 kcal/mol more stable than the anti-anti conformation, while the gauche-anti and anti-gauche are intermediate in energy. Since it is one of the smallest molecules exhibiting this effect, which has great interest in carbohydrate chemistry, dimethoxymethane is often used for theoretical studies of the anomeric effect.

Applications

Industrially, it is primarily used as a solvent and in the manufacture of perfumes, resins, adhesives, paint strippers and protective coatings. Another application is as a gasoline-additive for increasing octane number. Dimethoxymethane can also be used for blending with diesel.

Reagent in organic synthesis

Another useful application of dimethoxymethane is to protect alcohols with a methoxymethyl (MOM) ether in organic synthesis. Dimethoxymethane can be activated with phosphorus pentoxide in dichloromethane or chloroform. This method is preferred to the use of chloromethyl methyl ether (MOMCl). Phenols can also be MOM-protected using dimethoxymethane, p-toluenesulfonic acid. Alternatively, MOMCl can be generated as a solution by treating dimethoxymethane with an acyl chloride in the presence of a Lewis acid catalyst like zinc bromide:

MeOCH₂OMe + RC(=O)Cl → MeOCH₂Cl + RC(=O)(OMe)).

Unlike the classical procedure, which uses formaldehyde and hydrogen chloride as starting materials, the highly carcinogenic side product bis(chloromethyl) ether is not generated.