4,4 -diaminodiphenylmethane production

The technically important new fuchsine synthesis from a primary aromatic amine and formaldehyde falls, in the case of aniline, into the above reaction scheme since the formation of the intermediate product, p-diaminodiphenylmethane, is readily intelligible. 

The production of aniline is a major international business, carried on in the US, Europe and Asia, mainly for the conversion, by reaction with formaldehyde under acid-catalyzed conditions, into diaminodiphenylmethanes 9a, 9b and 9c, and then into isocyanates, mainly 4,4/-methylenebis(phenylisocyanate) (MDI, also known as 4,4 -methylene-di-paraphenylene isocyanate, 4,4 -diphenylmethane diisocyanate, methylene diphenylene diisocyanate and diisocyanato diphenyl methane) (9d), from which polyurethanes are produced. This accounts for well over 60% of total demand (Figure 1). Aniline is also used in bulk for the production of antioxidants and vulcanization accelerators for rubber. Some 15.5 million lbs. of cyclohexylamine are made each year mainly by catalytic hydrogenation of aniline. Half the demand is for use as a boiler water additive. Other major uses include in the manufacture of herbicides, plasticizers, emulsifying agents, dyes, dry-cleaning soaps, acid gas absorbents and, in Asia, cyclamate sweeteners. Apart from India, the use of aniline for dyestuff manufacture represents about 10% of demand. 

The first stage in the production of MDI (9d) is condensation between aniline and formaldehyde, in the presence of HC1, under subatmospheric pressure, at 70-105 °C. This affords 4,4, 2,4 and 2,2 isomers of diaminodiphenylmethane (9a, 9b and 9c). Reaction with phosgene in an inert solvent, such as chlorobenzene, first at low temperature, and then heating to 120 °C, gives, for the 4,4 isomer (9a), MDI, trimers, tetramers and higher oligomers, the latter known as poly-MDI or PMDI. Continuous liquid-phase phosgenation is favored. 

The reaction of trimellitic anhydride (7) with ethanolamine (9) giving the hydroxy acid (10) and with 4,4 -diaminodiphenylmethane (8) giving the diacid (11) has been published in the first poly(ester-imide) patent [l].The second one is nowadays the predominant reaction for making poly(ester-imide)s. Trimellitic anhydride is the basic dianhydride for introducing the imide structure into the polyesters. Nearly every example in patents is based on trimellitic anhydride alone or mixtures with other anhydrides, e.g., tetrahydrophthalic anhydride [59]. The imides made from aromatic anhydrides are thermally more stable than the ones resulting from aliphatic structures (Fig. 4). Both types have been protected by patents, and products made from them are on the market. 

The polymer industry requires large quantities of 4,4 -diaminodiphenyl-methanes. These compounds are used in various applications as polymer additives. Currently they are manufactured by the acid-catalysed condensation of anilines with formaldehyde but like so many reactions of this type, the processes require the neutralisation of waste acid leading to large amounts of salt waste. Cleaner processes are required and solid acids offer a way forward. One potentially useful example of this is the aqueous reaction of aromatic anilines adsorbed on kaolinite with formaldehyde which cleanly give the desired products (Figure 3.5).36 In a typical experiment, the clay is stirred with water before aniline is added to the stirred solution. To this is slowly added formaldehyde solution. The precipitated 4,4 -diaminodiphenylmethane can be extracted in hot ethanol in a yield of 96%. Similarly, several substituted analogues have been prepared in yields of 70-99%. 

Oxy-bis(iV-(4-phenylene)-trimellitic imide) is the product of condensation of trimellitic acid anhydride and 4,4 -diaminodiphenyl ether. Analogous bisimides can be prepared from trimellitic acid anhydride and MDI, 4,4 -diaminodiphenylmethane, or isophorone diamine. 

The most important commercial intermediates from aniline are the mixture of 4,4 - and 2,4 -diaminodiphenylmethane, obtained by reaction with formaldehyde, and the higher polyamines as well as 2-mercaptobenzothiazole and cyclohexyl-amine, used as rubber additives. N,N-Dialkylanilines are commonly used for the production of dyestuffs, while phenylhydrazine is used as an intermediate in the manufacture of plant protection agents, pharmaceuticals and dyestuffs. Other important aniline products are sulfanilic acid and acetanilide. 

Diaminodiphenylmethane is an aromatic diamine used as a curing agent in epoxy resins of the bisphenol A type, as in the production of plastics, isocyanates, adhesives, elastomers, polyurethane (elastic and rigid foams, paints, lacquers, adhesives, binding agents, synthetics rubbers, and elastomeric fibers) and butyl rubber. Diaminodiphenylmethane is also a by-product of azo dyes. It is also possibly formed by hydrolysis of diphenylmethane-4,4 -diisocyanate. 

Reyx, D. and Costes, B., Homopolymerisation of tetraglycidyl-4,4 diaminodiphenylmethane (TGDDM). Identification of cyclic reaction products. Polymer Commun., in press. 

The fluoride monomer is expensive and is generally made by Friedel-Crafts acylation from fluorobenzene or a diazotisation route from diaminodiphenylmethane. There are a number of patents which describe routes to difluorobenzophenone filed by companies such as Ihara, Raychem, Rhone Poulenc, Asahi and ICI, which can be found summarised in more recent patents [6, 7]. The recent work includes Victex s route from dinitrodiphenylmethane using tetramethylammoniumfluoride [7] and Inspecs s route [6] based on the reaction of formaldehyde with fluorobenzene followed by nitric acid oxidation of difluorodiphenylmethane. However, process economics will be driven by production scale and this gives an advantage to the existing producers and processes. 

In the first step, aniline is treated with formaldehyde in the presence of concentrated hydrochloric acid as catalyst. The product is a mixture of amines, composed mainly of 4,4 -diaminodiphenylmethane together with lesser amounts of the 2,4 -isomer and various poly amines with up to about 6 amino groups per molecule the polyamines have structures of the following type ... 

This sensitive reaction, which is used for the detection of manganese (see page 300), may also be used to detect periodates. The identification of small amounts of permanganate is accomplished by the use of tetrabase (tetramethyl-/>-diaminodiphenylmethane) a blue quinoidic oxidation product is formed (see page 280). Chlorates, bromates, and iodates do not interfere with the test. Persulfates react with manganese salts, giving... 

It will react with appropriate hardeners (aromatic amines, aliphatic amines, acid anhydrides) to produce a crosslinked product. Two hardeners of practical importance are triethylenetetramine and 4,4 -diaminodiphenylmethane... 

Figure 7.14 p,p -Diaminodiphenylmethane is synthesized from a condensation reaction product of aniline with formaldehyde... 

Poly(amide-imide)s are formed when a triacid derivative is treated with a diamine. The resulting polymer contains both amide and imide links. One such product is prepared from trimellitic anhydride (as the acid chloride) and 4,4 -diaminodiphenylmethane as shown on page 219. 

Bismaleimides can be polymerized directly through the double bonds at each end of the molecule but homopolymers prepared in this way tend to be very brittle. More useful products are obtained if chain extension involves a coreactant. A variety of compounds will add to bismaleimides but the most commonly used are diamines, e.g. 4,4 -diaminodiphenylmethane. Usual practice is to heat the bismaleimide with a molar deficiency of diamine at about 230°C under these conditions both addition of the amino group to the maleic double bond and direct interaction of double bonds occur simultaneously. This type of procedure is mostly used for the production of compression moulded printed circuit boards. 

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