Use and Manufacturing

1 Definition

ChEBI: A member of the class of formamides that is formamide in which the amino hydrogens are replaced by methyl groups.

2 Polymerization

Methylene diisocyanate polymerized violently on contact with dimethyl formamide.

3 Produe Method

Industrial production of N,N-Dimethylformamide (DMF) is via three separate processes (Eberling 1980). Dimethylamine in methanol is reacted with carbon monoxide in the presence of sodium methoxide or metal carbonyls at 110-150°C and high pressure. Alternately, methyl formate is produced from carbon monoxide and methanol under high pressure at 60-100°C in the presence of sodium methoxide. The resulting methyl formate is distilled and then reacted with dimethylamine at 80-100°C and low pressure. The third process involves reaction of carbon dioxide, hydrogen and dimethylamine in the presence of halogen-containing transition metal compounds to yield DMF.

4 Purification Methods

DMF decomposes slightly at its normal boiling point to give small amounts of dimethylamine and carbon monoxide. The decomposition is catalysed by acidic or basic materials, so that even at room temperature DMF is appreciably decomposed if allowed to stand for several hours with solid KOH, NaOH or CaH2. If these reagents are used as dehydrating agents, therefore, they should not be refluxed with the DMF. Use of CaSO4, MgSO4, silica gel or Linde type 4A molecular sieves is preferable, followed by distillation under reduced pressure. This procedure is adequate for most laboratory purposes. Larger amounts of water can be removed by azeotropic distillation with *benzene (10% v/v, previously dried over CaH2), at atmospheric pressure: water and *benzene distil below 80o. The liquid remaining in the distillation flask is further dried by adding MgSO4 (previously ignited overnight at 300-400o) to give 25g/L. After shaking for one day, a further quantity of MgSO4 is added, and the DMF is distillied at 15-20mm pressure through a 3-ft vacuum-jacketed column packed with steel helices. However, MgSO4 is an inefficient drying agent, leaving about 0.01M water in the final DMF. More efficient drying (to around 0.001-0.007M water) is achieved by standing with powdered BaO, followed by decanting before distillation, then with alumina powder (50g/L, previously heated overnight to 500-600o), and distilling from more of the alumina, or by refluxing at 120-140o for 24hours with triphenylchlorosilane (5-10g/L), then distilling at ca 5mm pressure [Thomas & Rochow J Am Chem Soc 79 1843 1957]. Free amine in DMF can be detected by the colour reaction with 1-fluoro-2,4-dinitrobenzene. It has also been purified by drying overnight over KOH pellets and then distilling from BaO through a 10 cm Vigreux column (p 11) [Jasiewicz et al. Exp Cell Res 100 213 1976]. [For efficiency of desiccants in drying dimethylformamide see Burfield & Smithers J Org Chem 43 3966 1978, and for a review on purification, tests of purity and physical properties, see Juillard Pure Appl Chem 49 885 1977.] It has been purified by distilling from K2CO3 under high vacuum and fractionated in an all-glass apparatus. The middle fraction is collected, degassed (seven or eight freeze-thaw cycles) and redistilled under as high a vacuum as possible [Mohammad & Kosower J Am Chem Soc 93 2713 1971]. [Beilstein 4 IV 171.] Rapid purification: Stir over CaH2 (5% w/v) overnight, filter, then distil at 20mmHg. Store the distilled DMF over 3A or 4A molecular sieves. For solid phase synthesis, the DMF used must be of high quality and free from amines.