GB1567114A - Process for the preparation of polyarylamines of the poly(aminophenyl)methane series - Google Patents

Description

(54) PROCESS FOR THE PREPARATION OF POLYARYLAMINES OF THE POLY(AMINOPHENYL) METHANE SERIES (71) We, BAYER AKTIENGESELLSCHAFT, a body corporate organised under tbe laws of Germany, of 509 Leverkusen, Germany; do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: this invention relates to a new process for the preparation of polyarylamines of the di henyl alkane series.

.The preparation of polyarylamines of the diphenyl alkane series is carried out according to the known art by condensing carbonyl compounds with the corresponding arylamines, particularly with the aid of acid catalysts. Numerous variations of this process are carried out on a technical scale for obtaining the appropriate compounds of the diamino diphenyl methane series. The most important representatives of this class of substances are the unsubstituted diamino diphenyl methanes condensed from aniline and formaldehyde.

It is a characteristic feature of the basic reaction outlined above that, in the conversion of the starting products to the end products by way of various intermediate stages, two new carbon-carbon bonds are formed at each stage between the carbonyl carbon atom and a ring carbon atom of two arylamine molecules, which may be regarded as stable in an aqueous medium at normal pressure under the conditions of an acid catalysed, arylamine-buffered reaction. The increased reactivity of the aryl nucleus in the ortho- and para- positions to the amino group explains the absence of meta-substituted products and the simultaneous occurrence of ortho- and para-substitution on both initial arylamine molecules built into the product in the course of the reaction. The possibility therefore always exists of all three possible substitution products, (A), (B) and (C), being formed from aniline and formaldehyde:

In an aqueous, acid catalysed condensation reaction, para-substitution always occurs preferentially to ortho-substitution so that the probability of formation increases from (A) to (C). The ratio of ortho-substitution to para-substitution may be influenced to a limited extent by adjustment of the reaction conditions, e.g. the degree of protonation when protonic acid is used as catalyst (percentage of protonated amino groups, based on the total number of amino groups), the condensation ratio (ratio of amine equivalents to carbonyl equivalents), the temperature profile of the reaction and quantity of water used, but it is not possible to reverse the above-described trend. This means that, according to the processes and methods known in the art, it is neither possible to completely suppress the formation of ortho-substitution products in the above reaction, nor is it possible to make them quantitatively the main products.

The increasing demand for highly pure 4,4'-diisocyanato diphenyl methane obtained from product (C) and the increasing importance of 2,4'-diisocyanato diphenyl methane obtainable by phosgenation of (B) necessitates complicated and expensive purification and separating operations at the diamino diphenyl methane stage or at the isocyanate stage in order to obtain the required pure or concentrated products.

The method of condensation of carbonyl compounds with arylamines fails completely when attempts are made to use it for producing asymmetric condensation products in virtually quantitative yields from two different starting arylamines, which condensation products are increasingly gaining in importance as starting materials for the preparation of the corresponding polyisocyanates and as starting materials for the preparation of the corresponding hydrogenated polyamines and of the polyisocyanates obtainable from these hydrogenated polyamines. The reason for this failure is that, while varying quantities of asymmetric product are produced, the formation of symmetric condensation products of the starting arylamines with the carbonyl compound cannot be suppressed.

For example, the simultaneous condensation of aniline and methyl aniline with for- maldehyde invariably gives rise to all three compounds (D), (E) and (F):

It is therefore an object of the present invention to provide a process for the controlled preparation of asymmetric polyamines of the diphenyl alkane series. This problem may be solved by the process according to the present invention which is described in more detail below. In addition, with suitable choice of the starting components, the process according to the present invention also enables symmetric polyamines of the diphenyl alkane series to be obtained in high yield and as very uniform products.

The present invention relates to a process for the preparation of polyarylamines of the diphenyl methane series, characterised in that (a.) aromatic compounds which carry at least one a-haloalkyl substituent and which have at least one nitro group in the ortho- and/or para- positions to the haloalkyl group are reacted with arylamines which carry no hydrogen atoms in the ortho- or para- positions to the amino group or with arylamines which carry no hydrogen atoms in the para- position to the amino group, the reaction resulting in the corresponding nitrobenzyl ary amines with the formation of hydrogen halide; the the hydrogen halide formed is removed in the form of a salt by neutralisation with base; (c.) the nitro group or groups of the condensation product obtained according to (a.) and (b.) is or are reduced to amino group (s) in known manner; (d.) arylamines which are more easily substituted in the nucleus than those used according to (a.) and which have at least one hydrogen atom on the aromatic nucleus in the ortho- and/or para- positions to amino group and/or acid salts of such arylamines are added to the product obtained from reaction step (c.); and (e.) the mixture obtained according to (d.) is caused to undergo molecular rearrangement to form polyarylamines of the diphenyl methane series in the presence of water and acid catalysts, the arylamine used according to (a.) being simultaneously liberated.

By the term "polyarylamines of the diphenyl alkane series" are meant, in the context of the present invention, in particular 2,2'-, 2,4'- and 4,4'-diamino diphenyl methanes, the corresponding diamines carrying one or two substituents, preferably C1-C4 alkyl groups, on a nitrogen atom, derivatives of the first-mentioned diamines substituted on one or both aromatic rings and/or derivatives thereof which carry one or two substituents on the methylene bridge. The following are examples of possible substituents of the aromatic rings: CnH2nz1 (n=1-4); CH2-C6Hs; C6Hs; OCH3; OC2Hs; SCH3; NH2; NH(CH3); NH(C2Hs); N(CH3)2; N(C2H5)2; CH2-C6H4-NH2; C1; Br; F; and/or COO CJI2a1 (n = 1-4). NH2, CH3 and/or 2-aminobenzyl or 4-aminobenzyl groups are preferred. Phenyl, benzyl and/or C,-Cl8 alkyl groups are possible substituents on the methylene bridge, phenyl, benzyl and methyl substituents being preferred.

The process according to the present inventon will first be illustrated with reference to the reaction of 2-nitrobenzyl bromide with mesidine in the first stage and aniline in the last stage.

CH3 CH2-Br + H2NCH3 N02 -HX CH3 CH3 CH3 N02 CH3 H2 (Raney - Nickel ) CH3 q 2 CH3 NH2 ss + / / HZN H2 C IT H2 NH2 H2N NH2 tCH24 NH2 When 2-nitrobenzyl bromide is condensed with mesidine (2,4,6-trimethyl aniline), the corresponding N-(2-nitrobenzyl)-2,4,6-trimethyl aniline is first formed, which is then converted into N-(2-aminobenzyl)-2,4,6-trimethyl aniline by catalytic hydrogenation.

After the addition of aniline in the required excess, the reaction is continued to the end product in the presence of water and an acid catalyst. In the preferred reaction, 2,4diamino diphenyl methane is formed in addition to small quantities of 2,2'-diamino diphenyl methane in the dinuclear fraction of the product, although the formation of 4,4'-diamino diphenyl methane, which is the main product of aniline-formaldehyde condensation, is completely excluded. When a 2,6-disubstituted aniline is used instead of aniline, the corresponding 2,4'-diamino diphenyl methane derivative is formed exclusively.

The following are suitable starting materials for the process according to the present invention: (1.) Any a-haloalkyl substituted aryl compounds which have at least one nitro group in the ortho- and/or para- positions to the haloalkyl group, provided these compounds are inert under the reaction conditions of the process according to the present invention, apart from the reactive groups which are essential to the present invention. Examples of suitable compounds of this type are particularly those corresponding to the following general formula:

wherein R1 and R2, which may be the same or different, each represents, preferably, hydrogen and/or a group corresponding to the substituents mentioned above in the description of the substituents for the methylene bridge; X represents chlorine or bromine; Y, Yl, Yii, which may be the same or different, each represents a nitro group or hydrogen, at least one of these groups and not more than two thereof representing a nitro group.

The following are examples of such compounds: 4-nitrobenzyl bromide, 2-nitrobenzyl bromide, 2,4-dinitrobenzyl bromide, 2,6-dinitrobenzyl bromide, a-phenyl-4-nitrobenzyl bromide, a-phenyl-2-nitrobenzyl bromide, 2-nitro-1,3-bis-bromomethyl benzene, 4-nitro-1,3-bis-bromomethyl benzene, 4-nitrobenzyl chloride, 2-nitrobenzyl chloride, 2,4-dinitro benzyl chloride, 2,6-dinitrobenzyl chloride, a-methyl-4-nitrobenzyl chloride, a-methyl-2-nitrobenzyl chloride, a,a-dimethyl-4-nitrobenzyl chloride, a,a-dimethyl-2- nitrobenzyl chloride and amethyl-2,4'-dinitrobenzyl chloride. Higher nuclear haloalkyl substituted aryl compounds conforming to the above definition, e.g. 1 chloromethyl-4-nitronaphthalene, are also suitable.

(2.) Compounds used for reaction with the above described a-haloalkyl-nitroaryl compounds (according to (a)) to form the corresponding nitrobenzyl arylamines are preferably those arylamine compounds in which the ortho- and para-positions are blocked by substituents which are inert under the conditions of the following reaction stages, particularly in rearrangement stage (e), in the sense that they cannot be substituted on the aromatic nucleus. Examples of such compounds include: 2-amino-1,3,5-trimethyl benzene, 2-amino-1,3-diethyl-5-methylbenzene, 2-amino-1,5-diethyl-3-methyl benzene, 2-amino- 1 ,5-dimethyl-3-benzyl benzene and 3,3',5,5' -tetramethyl-4,4' -diamino diphenyl methane. Considerable selectivity of the reaction for the purpose of the process according to the present invention may also be achieved with arylamines which are blocked only in the 4-position to the amino group. Examples of suitable compounds of this type include: 4-methyl aniline, 4-tertiary butyl aniline, 4-chloro aniline, 4-bromo aniline, 4-benzyl aniline and 4,4'-diamino diphenyl methane. Particularly advantageous results are obtained with these compounds if the arylamines added at (d) are more highly reactive, i.e. if they enter more readily into an electrophilic substitution on the aromatic nucleus than the arylamines mentioned for stage (a). This is true particularly of arylamines which are unsubstituted in the para-position to the amino group and/or those which are additionally activated by alkyl or amino substituents on the nucleus and by alkyl substituents on the nitrogen atom of the amino group(s).

(3.) Generally suitable for use according to (d), particularly when using those arylamines which are preferred for stage (a) are any arylamine compounds having primary, secondary or tertiary amino groups which compounds have at least one hydrogen atom which is bound to the aromatic nucleus in the ortho- and/or para- positions to an amino group and which compounds are inert under the conditions of the process according to the present invention, apart from the reactive centres which are essential to the present invention. Preferred arylamines of this type are those corresponding to the following general formula:

wherein R3 and R4, which may be the same or different, each represents, preferably, hydrogen or a group corresponding to the substituents mentioned in the description of the substituents on the aromatic rings; and R5 and R6, which may be the same or differnt, each represents hydrogen or an alkyl group having from 1 to 4 carbon atoms or a hydroxy-alkyl group, preferably hydrogen or a methyl or ethyl group.

The following are examples of suitable amines conforming to this definition: aniline, 2-amino toluene, 3-amino toluene, 4-amino toluene, 2-ethyl aniline, 2,6-dimethyl aniline, 2-isoproPyl aniline, 2,6-di-isopropyl aniline, N-methyl aniline, N-ethyl aniline, N,N- dimethyls aniline and N,N-diethyl aniline.

Apart from these preferred compounds which have been exemplified, diamines may also be used as arylamines conforming to the above definition, e.g. 4,4'-phenylene diamine, 2,4-diamino toluene and 2,6-diamino toluene, or arylamines carrying substituents other than those mentioned above, e.g. 2-chloroaniline, 2-methoxy aniline, 2-amino phenyl, 2-amino thiophenol, anthranilic acid Cl-C4 alkyl esters, 2,2'-, 2,4' or 4,4'-diamino diphenyl methane or 1,5- or 1,8-diamino naphthalene.

In general, when carrying out the process according to the Present invention, in the first stage (a), the starting materials mentioned under (1.) are reacted with the a famines mentioned under (2.) in the liquid phase at from 0 to 1000C, preferably from 30 to 80"C. The molar ratio of a-haloalkyl-nitroaryl compound to arylamine at this stage is generally from 1:1 to 20:1. If the arylamines, which are preferably used in excess, are liquids, they may serve as reaction medium and save time. Otherwise, it is advisable to add an inert hydrophobic solvent, such as dichloromethane, carbon tetrachloride, dichloroethane, ethylene chloride, trichloroethylene, diethyl ether, benzene, toluene, xylene or chlorobenzene. The disadvantage of halogen-containing solvents, which are particularly suitable as reaction media for stage (a) of the process according to the present invention, is that they must be removed before the catalytic reduction of the nitro-benzyl arylamine compound formed in the reaction.

The hydrohalic acid formed in the condensation reaction is removed in known manner in a second stage (b) of the process according to the present invention. This removal of hydrohalic acid is preferably carried out by reaction with an aqueous solution of a base, such as sodium bicarbonate, sodium carbonate or sodium hydroxide, followed by removal of the acid in the form of the sodium salt thereof. Reaction with aqueous ammonia solution and separation of the acid the ammonium salt is equally suitable.

Using water to wash out the hydrohalic acid after it has been neutralised to the aryl ammonium salt is the most suitable method because the salt solution thereby obtained may be used as catalyst for the molecular rearrangement step.

The third stage (c) of the process according to the present invention involves the known reduction of the nitro group(s) of the intermediate product obtained according to or) to the corresponding amino group(s) using known methods. Catalytic reduction using hydrogen in the presence of the conventional hydrogenation catalysts, e.g. Raney-Nickel, has proved to be particularly advantageous because of the mild reaction conditions employed with this method. The reduction may be carried out in excess arylamine as solvent or in an additional solvent, for example methanol. The reduction is generally carried out at from 30 to 100"C under a pressure of from 20 to 100 bar.

When reduction has been completed, the reduction catalyst is removed, for example, by filtration or by decanting the amine solution, and any auxiliary solvent used is preferably removed by distillation.

In the fourth stage (d) of the process according to the present invention, a second arylamine of the type examplified under (3.) is added in excess to the N-(arylmethyl)arylamine derivative obtained in the third stage (c) of the process according to the present invention. This second arylmine differs from the arylamines preferably used in stage (a) of the process according to the present invention, either in that it is unsubstituted on the aromatic nucleus in the ortho- and/or para- positions to at least one amino group or in that it is at least more easily substituted than the arylamine used according to (a).

In a further stage (e) of the process according to the present invention, the mixture obtained from stage (d) is caused to undergo rearrangement to the corresponding diaryl methane derivative in the presence of acid catalysts, the second arylamine added at (d) being built into the end product at this stage while the first arylamine used at (a) is removed unchanged. The rearrangement reaction may be carried out in the presence of a hydrophobic solvent of the type mentioned above, which is inert under the reaction conditions.

Suitable rearrangement catalysts are, in particular, water-soluble acids having a pKavalue of less than 2.5, preferably less than 1.5. Suitable acids include, for example, aqueous hydrochloric acid, hydrobromic acid, sulphuric acid, methane sulphonic acid, tnfluoroacetic acid and phosphoric acid.

Ion exchange resins having acid groups are also suitable. Aqueous hydrochloric acid and aqueous hydrobromic acid are particularly preferred. These acids may be used in the form of the aryl ammonium salts thereof. It is therefore particularly advantageous to use aqueous solutions of the aryl ammonium salts which may be obtained at stage (b) of the process according to the present invention.

The quantity of acid catalysts used may vary within wide limits and generally corresponds to a degree of protonation of from 10 to 100%, preferably from 20 to 50So. By "degree of protonation" is meant the percentage of all amine nitrogen atoms present as ammonium groups in the reaction mixture, including those in any excess arylamine which may have been added as reaction medium and including those in an aryl ammonium salt which may have been added as a catalyst.

The rearrangement reaction generally proceeds sufficiently rapidly when carried out in known manner at normal pressure and at temperatures above room temperature. It is preferably carried out at from 50 to 1000C, optionally at elevated pressure, and may even be carried out at temperatures above 100"C.

Working-up and isolation of the products obtained according to the present invention after the rearrangement reaction are carried out in known manner, for example by neutralisation of the catalyst with bases, such as aqueous sodium hydroxide solution, and/or by extraction of the products of the process from the aqueous reaction mixture with hydrophobic solvents, followed, in both cases, by distillation to purify the end product.

The total yield of the dinuclear diphenyl methane derivative may be increased in the last stage of the reaction by using a large excess of the second arylamine added in stage (b).

The yield of ortho- and para- isomers from the rearrangement reaction (e), corresponding to the formation of diamines (A) and (B) exemplified above may be varied within certain limits by the degree of protonation during the rearrangement reaction.

The formation of para-isomers (i.e. 2,4'-isomers) is favoured by an increase in the degree of protonation. It must be remembered, however, that even at low degrees of protonation the rearrangement into the para-position proceeds with higher yields if arylamines unsubstituted in the para-position were used in stage (b). Thus, for example, when 2-nitrobenzyl bromide and aniline are used as starting materials (in (e)), 2,4'd diamino diphenyl methane is invariably obtained as main product and 2,2' -diamino diphenyl methane as by-product. The formation of this by-product may, however, be kept within narrow limits by a high degree of protonation during rearrangement stage (e).

One important advantage of the process according to the present invention compared with known processes for the preparation of polyamines of the diphenyl methane series by aniline/formaldehyde condensation is therefore that it may be controlled to produce, 2,4'-diamino diphenyl methane in high yield. 2,4'-diamino diphenyl methane is a starting material for the preparation of the corresponding 2,4' -diisocyanato-diphenylmethane which is gaining progressively in importance in polyurethane chemistry.

The process according to the present invention may also be controlled to produce 4,4'-diamino diphenyl methane in high yields, for example when using 4-nitrobenzyl chloride in stage (a) and aniline in stages (d) and (e).

The superiority of the process according to the present invention over processes known in the art is shown particularly clearly in the controlled production of asymmetric diamino diphenyl methane derivatives, i.e. compounds such as those obtained as mixtures from the condensation of formaldehyde with two different arylamines.

Thus, for example, 3-methyl-4,4' -diamino diphenyl methane (E) may be obtained in excellent yields from 4-nitro-benzyl bromide and 2-amino toluene and the product obtained is free from the symmetric products (D) and (F).

Another particularly interesting feature of the process according to the present inven tion is the possibility of preparing 2,4' -diamino-diphenyl alkane derivatives corresponding to the following general formula:

wherein R1 and R2, which may be the same or different, each represents hydrogen or a methyl group; and R3 and R4, which may be the same or different, each represents hydrogen or an alkyl group having from to to 4 carbon atoms, at least one of the groups R3 and R4 being such an alkyl group; or a 4-amino benzyl or 2-amino benzyl group.

In particular the diamines having primary amino groups obtainable according to the present invention are valuable starting materials for the preparation of the correspondmg polyisocyanates.

Due tote possibility of preparing particular diisocyanates from diamines obtained according to the present invention, new perspectives are opened up for a controlled modification of the properties of polyurethane resins produced from these diisocyanates The products obtained according to the present invention which have primary and/or secondary and/or tertiary amino groups also constitute valuable chain-lengthening agents for the synthesis of polyurethanes and valuable tertiary amines which may be built into the polyurethanes.

Example I (A) 648 g (3.0 mol) of 2-nitrobenzl bromide are stirred into 1350 g (10 mol) of 2-amino-1,3,5-trimethyl benzene (mesidine).

The mixture is then heated to from 70 to 800C for 2 hours and maintained at this temperature before it is washed three times with one litre portions water, mesidinehydrobromide being thereby dissolved in the water. The organic phase is freed from traces of acid by the addition of 200 ml of dilute aqueous sodium bicarbonate solution and again washed with water.

(B) The major portion of excess mesidine is then distilled off in a water jet vacuum and the residue is taken up in 3500 ml of methanol and after the addition of 40 g of Raney-Nickel, it is reduced with hydrogen at 50 bar and from 50 to 70"C until uptake of hydrogen ceases. After removal of the Raney-Nickel by filtration, most of the methanol is distilled off. (White shimmering crystals may be obtained from methanol by recrystallisation: N- (2-aminobenzyl)-2,4,6-trimethyl aniline (m.p. 90-91"C)).

(C) The residue is taken up in 1529 g (16.5 mol) of aniline and the solution is then stirred into an approximately 3.5 molar aniline hydrochloride solution (6.5 litres).

The mixture is boiled under reflux for two hours. It is then made alkaline using aqueous sodium hydroxide solution and the aqueous phase is separated off and discarded.

Mesidine and excess aniline are distilled from the organic phase and separated.

The residue, amounting to 531 g (89.3% of the theoretical yield), has the following composition (gas chromatography): 2,2'-diamino diphenyl methane 8.2 %, by weight 2,4'-diamino diphenyl methane 79.6 %, by weight trinuclear triamines 11.5 %, by weight higher polyamines 0.7 %, by weight The amine mixture may easily be converted into the corresponding mixture of isocyanates by phosgenation.

Example 2 This is the same as Example 1, except that the residue from reducing stage (B) is added to 12 litres of a 3.5 molar aniline hydrochloride solution and boiled under reflux for two hours. It is then worked-up as in Example 1. The residue (510 g = 84.3 % of the theoretical yield) has the following composition: 2,2'-diamino diphenyl methane 4.9 So, by weight 2,4'-diamino diphenyl methane 70.0 So, by weight 2,4'-diamino diphenyl methane 70.0 %, by weight trinuclear triamines 21.4 So, by weight higher polyarylamines 3.7 %, by weight Example 3 The same as Example 1, but the residue from the reduction stage (B) is added to 12 litres of a 3.5 molar (42 mol) aqueous hydrochloride solution of ortho-toluidine. It is then boiled under reflux for 2 hours and worked-up as in Example 1. The residue (570 g = 89.6 % of the theoretical yield) has the following composition (gas chromatography): 3-methyl-2' ,2-diamino diphenyl methane 0.9 %, by weight 3-methyl-2' ,4-diamino diphenyl methane 81.4 %, by weight trinuclear triamines 15.9 %, by weight higher polyarylamines 1.8 %, by weight Example 4 The same as Example 1, but the residue is taken up in 5082 g (42 mol) of 2,6dimethyl aniline, 1190 ml (11.25 mol) of 30 % hydrochloric acid and 2 litres of water are added to the solution with cooling and the solution is the boiled under reflux for 2 hours. The reaction mixture is worked-up as in Example 1. According to gas chromatography, 97 % of the product obtained (m.p. 103-104 "C, 637 g = 94 % of the theoretical yield) consists of 3,5-dimethyl-2,4'- diamino diphenyl methane.

Example 5 The same as in Example 1, except that, in reaction stage (A), 648 g (3.0 mol) of 4-nitrobenzyl bromide are reacted with 1350 g (10 mol) of mesidine. The resulting product obtained as residue in reduction stage (B) is liquid. To it are added, with stirring, first 2890 g (27 mol) of ortho-toluidine and then, with cooling, 1272 mol of concentrated hydrochloric acid diluted with 2400 mol of water. The mixture is then boiled under reflux for 2 hours. The product is worked-up as in Example 1. It is obtained as distillation residue (606 g = 95.3 % of the theoretical yield, m.p. approximately 125"C).

According to gas chromatography, it has the following composition: 3-methyl-2,4' -diamino diphenyl methane 2.5 So, by weight 3-methyl-4,4' -diamino diphenyl methane 96.2 %, by weight higher polyaryl polyamines 1.3 %, by weight Example 6 The same as Example 1, but, in reaction stage (A), 648 g (3.0 mol) of 4-nitrobenzyl bromide are reacted with 1350 g (10 mol) of mesidine. The product obtained as residue in reduction stage (B) is liquid. It is stirred, first with 1452 g (12 mol) of 2,6-dimethyl aniline and then, under conditions of cooling, with 475 ml of 36 % hydrochloric acid and 2500 ml of water. The mixture is then boiled under reflux for 2 hours. The product is worked-up as in Example 1. It is obtained as distillation residue (m.p. 111"C,648 g = 95.6 % of the theoretical yield). According to gas chromatography, 99.5 % of this residue consists of 3,5-dimethyl-4,4'-diamino diphenyl methane.

WHAT WE CLAIM IS: 1. A process for the preparation of a polyarylamine of the diphenyl methane series which comprises: (a) reacting an aromatic compound having at least one a-haloalkyl substituent and having at least one nitro substituent in the ortho- and/or para-

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. Example 3 The same as Example 1, but the residue from the reduction stage (B) is added to 12 litres of a 3.5 molar (42 mol) aqueous hydrochloride solution of ortho-toluidine. It is then boiled under reflux for 2 hours and worked-up as in Example 1. The residue (570 g = 89.6 % of the theoretical yield) has the following composition (gas chromatography): 3-methyl-2' ,2-diamino diphenyl methane 0.9 %, by weight 3-methyl-2' ,4-diamino diphenyl methane 81.4 %, by weight trinuclear triamines 15.9 %, by weight higher polyarylamines 1.8 %, by weight Example 4 The same as Example 1, but the residue is taken up in 5082 g (42 mol) of 2,6dimethyl aniline, 1190 ml (11.25 mol) of 30 % hydrochloric acid and 2 litres of water are added to the solution with cooling and the solution is the boiled under reflux for 2 hours. The reaction mixture is worked-up as in Example 1. According to gas chromatography, 97 % of the product obtained (m.p. 103-104 "C, 637 g = 94 % of the theoretical yield) consists of 3,5-dimethyl-2,4'- diamino diphenyl methane. Example 5 The same as in Example 1, except that, in reaction stage (A), 648 g (3.0 mol) of 4-nitrobenzyl bromide are reacted with 1350 g (10 mol) of mesidine. The resulting product obtained as residue in reduction stage (B) is liquid. To it are added, with stirring, first 2890 g (27 mol) of ortho-toluidine and then, with cooling, 1272 mol of concentrated hydrochloric acid diluted with 2400 mol of water. The mixture is then boiled under reflux for 2 hours. The product is worked-up as in Example 1. It is obtained as distillation residue (606 g = 95.3 % of the theoretical yield, m.p. approximately 125"C). According to gas chromatography, it has the following composition: 3-methyl-2,4' -diamino diphenyl methane 2.5 So, by weight 3-methyl-4,4' -diamino diphenyl methane 96.2 %, by weight higher polyaryl polyamines 1.3 %, by weight Example 6 The same as Example 1, but, in reaction stage (A), 648 g (3.0 mol) of 4-nitrobenzyl bromide are reacted with 1350 g (10 mol) of mesidine. The product obtained as residue in reduction stage (B) is liquid. It is stirred, first with 1452 g (12 mol) of 2,6-dimethyl aniline and then, under conditions of cooling, with 475 ml of 36 % hydrochloric acid and 2500 ml of water. The mixture is then boiled under reflux for 2 hours. The product is worked-up as in Example 1. It is obtained as distillation residue (m.p. 111"C,648 g = 95.6 % of the theoretical yield). According to gas chromatography, 99.5 % of this residue consists of 3,5-dimethyl-4,4'-diamino diphenyl methane. WHAT WE CLAIM IS:

1. A process for the preparation of a polyarylamine of the diphenyl methane series which comprises: (a) reacting an aromatic compound having at least one a-haloalkyl substituent and having at least one nitro substituent in the ortho- and/or para- positions to the said a-haloalkyl substituent with an arylamine not having hydrogen atoms in the ortho- or para-positions to an amino substituent or with an arylamine not having a hydrogen atom in the para-position to an amino substituent to form the corresponding nitrobenzyl arylamine and hydrogen halide; b) removing the hydrogen -halide in the form of a salt formed by the addition of base; c) reducing the nitro group(s) of the nitrobenzyl arylamine to amino group(s); d) adding to the product of step (c) an arylamine which is more readily substituted on the nucleus than the arylamine used in step (a) and which has at least one hydrogen atom in the ortho- and/or para- positions to an amino substituent or an acid salt thereof; and (e) causing the mixture from step (d) to undergo molecular rearrangement in the presence of water and an acid catalyst to form a polyarylamine of the diphenyl methane series and to liberate the aryl-amine used in step (a).

2. A process as claimed in claim 1 substantially as herein described.

3. A process as claimed in claim 1 substantially as herein described with reference to any one of the Examples.

4. A polyarylamine of the diphenyl methane series when prepared by a process as claimed in any of claims 1 to 3.