“2-Methylglutaronitrile”的意思、由来-开放百科全书

2-Methylglutaronitrile (α-methyl-valerodinitrile) is a nitrile with an attached methyl group which is obtained in the large-scale synthesis of hexanedinitrile.

It is the starting compound for the vitamin nicotinamide and for the diester dimethyl-2-methylglutarate and the ester amide methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate, which are propagated as green solvents.

Occurrence and production

2-Methylglutaronitrile is a by-product of the production of hexanedinitrile, the precursor of hexamethylenediamine and hexanedioic acid as building blocks for polyamide 6.6.

Starting from 1,3-butadiene or a butadiene-rich C4-section (> 40% by volume) from a naphtha steamcracker in the first stage a mixture of pentenenitriles is obtained through hydrocyanation (using as catalyst Ni⁰-phosphine [PR₃]^[1] or phosphite or phosphonite [P(OR)₂R]^[2]). The mixture contains mainly trans-3-pentenenitrile in addition to the isomers 2-methyl-2-butenenitrile, 4-pentenenitrile and 2-pentenenitrile.

The mixture of monoolefinic C5 mononitriles is isomerized to 3- and 4-pentenenitrile with a hydrocyanation catalyst and a Lewis acid (such as ZnCl₂).^[2] In the third step, the mixture is reacted with hydrogen cyanide to give a mixture of dinitriles which contains in addition to 2-methylglutaronitrile also hexanedinitrile (adiponitrile) and 2-ethylbutanedinitrile.

The 2-methylglutaronitrile-rich fraction has hitherto been combusted as an undesired by-product of hexanedinitrile production, having the typical composition of about 86 wt% 2-methylglutaronitrile, 11 wt% 2-ethylbutanedinitrile and 3 wt% hexanedinitrile.^[5]^[4]

Properties

2-Methylglutaronitrile is a very unpleasant smelling, clear, colorless to brown liquid with low vapor pressure and a liquid range of >300 °C. The compound is very toxic, especially when inhaled.^[5]

Applications

2-methylglutaronitrile can be converted to 3-methylpyridine (β-picoline) by reaction with hydrogen on platinum or palladium contacts at temperatures of from 250 to 400 °C.^[6]^[7]

In addition to 3-methylpyridine, 3-methylpiperidine is obtained as a by-product from which further 3-methylpyridine can be obtained by dehydrogenation.

Ammonoxidation of 3-methylpyridine on transition metal contacts yields 3-cyanopyridine (nicotinonitrile) in yields of 95%.^[8]

Hydrogenation of a solution of 2-methylglutaronitrile in ethanol in the presence of Raney cobalt at 15 bar and 100 °C yields 2-methylpentane-1,5-diamine.^[14]

2-Methylpentanediamine can be converted to 3-methylpiperidine at 300 to 400 °C on a zeolite contact and then dehydrated on a palladium contact to 3-methylpyridine, which can be converted via nicotinonitrile into nicotinamide.^[8]

The racemic diamine can also be used for the preparation of specific polyamides and after reaction with phosgene to form 2-methylpentane diisocyanate^[15] as a reaction component in polyurethanes. Nitrilases regioselectively hydrolyze the ω-nitrile group in α, ω-dinitriles without detectable amide intermediate directly to the carboxyl group. 4-cyanopentanoic acid is formed in high yield.^[16]

The ammonium salt of 4-cyanopentanoic acid can be converted by catalytic hydrogenation in the presence of methylamine in 1,5-dimethyl-2-piperidone,^[17]^[18] an environmentally compatible solvent.^[19]

The hydrolysis of both nitrile groups of 2-methylglutaronitrile with e.g. 20% sodium hydroxide solution at 50 °C and subsequent acidification produces 2-methylglutaric acid.^[20]

Starting from 2-methylglutaronitrile the hydrolysis to 2-methylglutaric acid can also be accomplished via the 2-methylglutarimide obtained by heating a 2-methylglutaronitrile/water mixture to 275 °C in the presence of a titanium dioxide catalyst in yields of 94%.^[21]

The reaction of 2-methylglutarimide with e.g. methanol (methanolysis) produces the diester dimethyl-2-methylglutarate^[22] in the presence of titanium dioxide^[23] or lanthanum oxide.^[24] It was commercialized as an environmentally friendly aprotic dipolar solvent under the name Rhodiasolv® IRIS with the typical composition 87-89% dimethyl-2-methylglutarate, 9-11% dimethyl 2-ethylbutanedioate and 1-2% dimethyl hexanedioate^[4] as a substitute for acetone, dichloromethane, N-methylpyrrolidone and the like.

The ester mixture is very similar to so-called dibasic esters, which are commercially available as FlexiSolv® DBE® esters.^[25]

The diester can be selectively converted into a mixture of 1- or 5-substituted methyl ester amides with dimethylamine in methanol/sodium methoxide,^[26] which is used under the name Rhodiasolv® Polarclean as formulation auxiliaries for crop protection preparations.^[4] The resulting ester amides are readily biodegradable and good solvents for a variety of different plant protection agents (such as insecticides or fungicides), also compared to the frequently used N-methylpyrrolidone, cyclohexanone or isophorone.

Other esteramides are derived, e. g. from 2-methylglutaronitrile which, after alkaline hydrolysis, is converted into 2-methylglutaric acid, cylized with acetic anhydride to give 2-methylglutaric anhydride, reacted with dimethylamine to form the monoamide, reacted to an acid chloride with thionyl chloride and formed to an ester with more hydrophobic alcohols (like butanols or cyclohexanol).^[27]

References

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