Module: 7 Lecture: 36 DIMETHYL FORMAMIDE INTRODUCTION Dimethylformamide is an organic compound and denotes as DMF. The name is derived from the fact that it is a derivative of formamide, the amide of formic acid. It is a colourless polar solvent and miscible with water and the most of the organic liquids. Pure dimethylformamide is odourless while technical grade or degraded dimethylformamide has a fishy smell due to impurity of dimethylamine. The first time N-alkylformamides were produced in 19 th century. In 1899, BEHAL produced N-alkylformamides by help of mixed anhydride of formic acid and aliphatic acids. After that N-dimethylformamide was synthesized by using hydrocyanic acid and methanol or methylamines in the presence of water. As it having a high boiling point, it facilitates reactions which follow polar mechanisms, such as SN 2 reactions. Dimethylformamide can be synthesized from methyl formate and dimethylamine or by reaction of dimethylamine with carbon monoxide. It is not stable in the presence of strong bases like sodium hydroxide or strong acids. It may be hydrolyzed back into formic acid and dimethylamine at elevated temperatures. MANUFACTURE Raw material Basis: 1000kg dimethyl formamide from methyl amine (98% yield) Dimethyl amine 605kg Carbon monoxide 380kg N P T E L 1
Reaction Manufacture process Pure carbon monoxide or a gas stream containing carbon monoxide was passed into the reactor. Sodium methoxide Water Methanol Dimethyl formamide Dimethyl amine Product column CO Reactor Settling tank Salt Evaporator Light end column Salt Figure: Manufacture of dimethyl formamide from methyl amine Block diagram of manufacturing process Diagram with process equipment Animation The continuous liquid dimethylamine were introduced to the reactor in presence of sodium methoxide in methanol as catalyst. The pressure and temperature was maintained between 0.5 11MPa and 50 200 0 C respectively. The reaction is exothermic and reversible there so, it was carried out in the liquid phase at high pressure, with a slight excess of carbon monoxide. The catalyst was reacted with by-products in the gaseous feed stream, such as carbon dioxide and water, which formed solid salts. These salts were water soluble, so periodically, when the salt deposits build up, the reactor has to be taken off line and washed out. N P T E L 2
Crude dimethylformamide from reactor was transferred to a settling tank where it was added with water to prevent further reaction, salts were allowed to settle out, and then the liquid phase was charged to an evaporator, which vaporised the dimethylformamide and removed the small amount of salt from bottom. Hot vapour from evaporator was fed to the light ends column, where methanol, water and any residual trace dimethyl amine were removed. The dimethylformamide separated from methanol which containing traces of N,N-dimethylamine was pumped into the product column, and the refined dimethylformamide was taken off as an overhead stream as 99.9% purity. Environmental protection In the case of fire around DMF plant, it has to be extinguished with water, dry chemical agents, or carbon dioxide. N,N-dimethylformamide is considered as a hazardous liquid respect to water pollution. So, the direct discharge of DMF into streams and lakes must be avoided. Nevertheless, it is easily biodegradable in waste water treatment plants. DMF emissions exceeding 3kg/hr must be diluted; otherwise the corresponding off-gases must be treated with water or combusted. The content of DMF in air can be measured by gas chromatography or with an infrared detector. Quality specification and analysis High purity DMF is required for any applications. By potentiometric titration the acid and base content of the DMF sample was established. The method for determining DMF depends upon the anticipated concentration: those above 10% may be quantified gas chromatography, while lower concentrations were best measured with a double beam infrared photometer. If traces of DMF air expected as in wastewater, then a combination of chemical physical methods has to be employed. So, DMF can be hydrolyzed with acid. After that the solution was made alkaline and the resultant N,Ndimethylamine was distilled. DMF content can be calculated using refractive index or density. N P T E L 3
Engineering aspects DMF plant with CO as a raw material does not preferred if some problems occurs in the CO separation unit otherwise CO route can be used. Efforts for absorbing technology and making further improvements were only possible when the plant has been properly designed. The reaction of formamide and methanol was carried out as an alternative route to produce DMF. This process gives better yield and lower cost of production per unit production of DMF. PROPERTIES Molecular formula : C3H7NO Molecular weight : 73.09gm/mole Appearance : Colourless liquid Odour : Fishy, ammoniacal odour Boiling point : 152-154 0 C Melting point : -60.0 0 C Flash point : 58.0 0 C Autoignition temperature : 445 0 C Refractive index : 1.430 at 20 0 C Density : 1.97gm/cm 3 Solubility : Miscible with water USES N, N-dimethylformamide used as a solvent and as an extractant, particularly for salts and compounds with high molecular mass As catalyst in synthesis of acyl halides, particularly in acyl chloride from carboxylic acid using thionyl chloride Effective at separating and suspending carbon nanotubes It can be utilized as a standard in proton NMR allowing for a quantitative determination of an unknown chemical To recover olefins such as 1,3-butadienevia extractive distillation In the manufacturing of solvent dyes as an important raw material Industrial acetylene gas is dissolved in DMF and stored in metal cylinders As a solvent for polymers in the preparation of polyacrylonitrile solutions N P T E L 4
for the manufacture of fibrous polyacrylonitrile and polyurethane As a solvent for coating surfaces and wire enamel formulated with polyamides, polyesterimides, in peptide coupling for pharmaceuticals, in the development and production of pesticides, in the manufacturing of adhesives, synthetic leathers and films As a selective solvent in a wide range of manufacturing process viz. in separating acetylene from ethylene; butadiene from C4cuts; and hydrogen chloride, hydrogen sulfide, or sulfur dioxide form CO2 containing gases Its solubilizing ability also makes it an effective component of paint removers Used by oil refiners to extract aromatic compounds from hydrocarbon mixtures Solutions of salts in specially purified DMF serve as fillers for electrolytic capacitors, a role made possible by the high dielectric constant of DMF In the synthesis of aldehydes, acetals, amides, amidines, esters, and heterocycles N P T E L 5