Dimerization of acrylonitrile

The Monsanto adiponitrile process, first commercialized in 1965 (65—67), involves the dimerization of acrylonitrile at the cathode in an electrolytic cell (eq. 7) ... 

A. Nucleophilic Attack on Carbon. —(/) Activated Olefins. A study of triarylphosphine-catalysed dimerization of acrylonitrile to 2-methylene-glutaronitrile (26) and 1,4-dicyano-l-butene (27) has established a balance between phosphine nucleophilicity and protolytic strength of the solvent. The reaction of methyl vinyl ketone with triphenylphosphine in triethyl-silanol gave only 3-methylene-2,6-heptadienone (28). 

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

CANDID A process for making adiponitrile by reductive dimerization of acrylonitrile. Invented by ICI in 1976 and piloted in the United Kingdom from 1986, but not commercialized. 

Isopropyl diarylphosphinites (Ar2POPr ) catalyse the dimerization of acrylonitrile to a mixture of cis- and fra 5 -l,4-dicyanobut-l-ene (136), rrani-l,4-dicyanobut-2-ene (137), and 2,4-dicyanobut-l-ene (138). The kinetics and mechanism of the reaction. 

It is interesting to note that reduction of cinnamonitrile, related to aromatic nitriles, gives dimers. Electrochemical dimerization of acrylonitrile is a well-known industrial process of the... 

The kinetics and mechanism of the phosphorus-catalysed dimerization of acrylonitrile to give 1,4-dicyanobut-l-ene and 2,4-dicyanobut-l-ene have been studied.114 The reactions of aryhminodimagnesium (138) with //-substituted p-cyanobenzophenones, l-cyano-9-fluorenenone, o-, m-, and p-dicyanobcnzcnes, and o-, m-, and p-nitrobenzonitriles have been examined.115 The effect of pressure on the reaction of 3 -methyl- l-(4-tolyl)triazene (139) and benzoic acid in chloroform and acetonitrile has been studied.116 The effect of acids on the rate of urethane formation from alcohols and isocyanates in the presence of alkyltin carboxylates has been examined.117 A Hammett a value has been reported for the amidine group N=CHNMe2 and used for the prediction of the basicity of sites in bifunctional amidines.118... 

The tail-to-tail dimerization of acrolein [3] and acrylonitrile [4, 5] was also obtained, with a lower reactivity and stereoselectivity. However, the dimerization of acrylonitrile was performed under mild conditions in the presence of molecular hydrogen with Ru(COD)(COT), where COT is cyclooctatetraene, [4] (Eq.2). 

The dimerization of acrylonitrile is a cheaper route to the synthesis of highly valuable hexamethylenediamine, which is one component of the starting materials for nylon-6,6 [ 16,35] In some cases of the dimerizations of acrylic acid... 

However, the photocycloaddition of ketones to Z-substituted alkenes does not fit the explanation based on the relative stability of the diradicals. Irradiation of a solution of acrylonitrile 8.22 in acetone 8.21 gives the adduct 8.23, together with dimers of acrylonitrile. This regioselectivity is consistent with a frontier orbital argument. 

Less well defined catalysts, such as RuCl2(DMSO)4/carboxylic acid, catalyze the linear tail-to-tail dimerization of acrylonitrile.133... 

Stereochemical studies add great support to the proposition that [2 + 2] cycload tions involve tetra-methylene diradical intermediates, for these additions e place with partial or complete loss of cis/trans stereochemical relationships present in alkene reactants, llie dimerization of acrylonitrile, for example, studied with ci5-l,2-dideuteriocyanoethylene (42), gives six distinct [2 + 2] adducts the distribution of deuterium labels in the df-l,2-dicyanocyclobutane products are given in structures (43), (44) and (45) an analogous set of three trans stereoisomers is formed. Recovered starting material shows partial loss of stereochemical integrity. 

Catalytic dimerization of acrylonitrile with RuCls SHgO in ethanol at 150°C under hydrogen pressure yields a yellow complex considered (413) to be a metal-olefin tt complex, while the corresponding reaction under nitrogen pressure produces only the nitrogen-bonded complex (CH2CHCN)3RuCl3. The former complex itself catalyzes the dimerization reaction (413)... 

The first sodium amalgam-induced dimerization of acrylonitrile to adiponitrile [29] was performed in aqueous solution, and the yield was discouragingly low (5%). Mainly, a base-induced addition of water resulting in p, -bis(cyanoethyl) ether occurred together with a reduction to propionitrile (PN). 

Cramer studied the mechanism using Rh compounds [123, 124], The linear dimerization of acrylonitrile in the presence of hydrogen and a ruthenium catalyst to form 1,4-dicyano-l-butene [125-127] received much interest in industrial laboratories, mostly in Japan, so a large number of patents have been filed, in some of which palladium catalysts have also been claimed. The above compound can be hydrogenated to give the industrially important adipodinitrile and hexa-methylene diamine. 

However, the photocycloaddition of ketones to Z-substituted olefins is anomalous if this argument is used but their behaviour is entirely consistent with the frontier orbital argument. Irradiation of acrylonitrile (469) in acetone (468) solution gives the adduct (470), together with dimers of acrylonitrile.378... 

Electrochemical processes are often touted as being green chemistry because electricity is considered inexpensive, and toxic metal reagents are usually avoided. Electrochemical processes have produced tons of bulk chemicals [37], the best-known of which may be adiponitrile from reductive dimerization of acrylonitrile (Figure 13.17) [38]. An electrochemical synthesis to manufacture fenoprofen is shown in Figure 13.18, with the magnesium provided as a sacrificial electrode [39], Flow cell technology has been used for these operations on a commercial basis. 

Dimerization of acrylonitrile is a cheaper way to synthesize highly valuable hexamethylenediamine [30]. In some cases of dimerization of acrylic acid esters, acrylonitriles, and acroleins, the direct C-H bond cleavage step seems to be involved in the catalytic reaction. At an early stage of catalytic dimerization of acrylonitrile, czs-l,4-dicyanobut-l-ene is formed as the major product, not trans-isomer [31]. This high czs-selectivity is suggested to indicate selective cleavage of C-H cis to CN by the metal coordinated to the nitrile group in side-on fashion. 

Scheme 5.7 Reductive dimerization of acrylonitrile (Baizer-Monsanto process)...

This involves the dimerization of acrylonitrile with hydrogenation. This techniquewas developed by an electrochemical method in the 1960s by Monsanto and commercialized as the EHD (Electro Hydro Dimerization) process. Other companies, manufacturers of nylon-6,6, have proposed a number of variants, including Asahi, Du Pont. Hakon, 1CI and UCB (Union Chimiqae Beige). 

Solvent Manufacture and Preparation. 1,3-Dicyanobutane is a new material which can be produced at low cost by a process developed in the laboratories of U. S. Industrial Chemicals Co. (6, 7,14). The catalytic dimerization of acrylonitrile produces methyleneglutaronitrile which is readily hydrogenated to give methylglutaronitrile, also called 1,3-dicyanobutane. Thus,... 

Processes 4, 5, and 6 in Figure 2.13 are based on acrylonitrile. Among them, process 6 is the oldest. Introduced in 1965 as a technical process by Monsanto [175], it involves the electrolytic dimerization of acrylonitrile to adiponitrile. The process is carried out in a system of electrolytic cells containing sulfonated polystyrene membranes. An aqueous solution of tetraethylammonium- -toluyl sulfonate is used as the catholyte and aqueous sulfuric add as the anolyte. Using a 40% aqueous solution of acrylonitrile at temperatures of 25 35°C, the following reaction sequences occur ... 

Processes 4 and 5 in Figure 2.13 are more recent developments entailing dimerization of acrylonitrile. Although formally analogous to the Monsanto process they are quite different because they proceed via catalysis rather than electrolysis. One of these processes developed by Halcon [176] involves liquid-phase reaction of acrylonitrile at 30°C under a nitrogen pressure of 0.7 MPa in the presence of a two-component catalyst system. 

Figure 6.2 The early Monsanto process for the hydro dimerization of acrylonitrile,...

Figure 6.5 Flow sheet for Monsanto hydro dimerization of acrylonitrile to adiponitrile, AN, acrylonitrile ADN, adiponitrile QS, tetraethylammonium ethylsulphate.

Figure 6.7 Possible reaction pathways for the hydro dimerization of acrylonitrile to adiponitrile. The asterisk indicates that electron transfer can be from the cathode or from [CH2CHCN] in homogeneous solution.

However, the most significant changes in nylon-6, 6 production lie in the newer routes to adiponitrile introduced by Monsanto and Du Pont into both the U.S.A. and Western Europe. The former entails the electroreductive dimerization of acrylonitrile, while Du Pont use the addition of HCN to 1,3-butadiene catalysed by Ni(0) complexes ... 

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