WO1988004296A1

WO1988004296A1 - Colour former manufacture

Info

Publication number: WO1988004296A1
Application number: PCT/GB1987/000871
Authority: WO
Inventors: Kenneth John Shanton
Original assignee: The Wiggins Teape Group Limited
Priority date: 1986-12-03
Filing date: 1987-12-03
Publication date: 1988-06-16
Also published as: JPH01501484A; EP0292522A1; GB8628914D0

Abstract

Method for the preparation of a lactone colour former by reacting a substituted ethylene with a cyclic aromatic carboxylic anhydride or an intermediate keto acid derived from prior reaction between the anhydride and an aromatic compound, in the presence of a dehydrating agent, wherein following the reaction the solid reaction product formed is separated and washed in an alkaline polar organic solvent with removal of acid or potentially acid materials and of coloured by-products where present.

Description

COLOUR FORMER MANUFACTURE

The invention relates to the manufacture of colour formers useful in pressure or heat sensitive record material e.g. carbonless copy paper and thermal paper.

A common synthetic route to chromogenic-lactone colour formers is an overall dehydration condensation between a cyclic carboxylic acid anhydride, which contributes the lactone ring to the product, and one or two compounds each having a reactive hydrogen atom, which contribute the remaining residues of the (potential) chromophore. This route can conveniently be regarded as a two stage reaction, illustrated as follows (with phthalic anhydride as the cyclic carboxylic acid anhydride):

where A and B are the desired residues in the (phthalide) product. The residues A and B can be the same or different and one, usually both, is generally a nitrogen containing radical, particularly an aromatic amine or a heterocyclic radical such as indolyl. When A and B are different the reaction will usually be carried out in two separated steps. Where A and B are identical the reaction may be carried out without isolation of intermediates, the keto-acid being generated in situ for the second reaction step.

Step ii of such a synthesis is carried out under dehydration conditions, typically in the presence of a dehydrating agent which is very commonly a liquid carboxylic acid anhydride, especially acetic anhydride. The dehydrating agent will be used in excess of the stoichiometric requirement and may also act as the reaction medium. In such cases, as the reaction proceeds the anhydride is converted into the corresponding carboxylic acid.

Recovery of the product from the reaction mixture can be effected by quenching into water or ice and subsequently isolating the colour former product from the work-up mix. However, some colour formers have limited solubility in the reaction medium and are desirably separated directly by filtration or centrifuging.

A difficulty experienced in such direct isolation of the product is in securing complete removal of both the acid by-product and, especially, the (potentially acid) anhydride dehydrating agent. Traces of these materials left in the product appear to sensitise it towards premature coloration e.g. during encapsulation (for pressure sensitive record material), although the degree of residual acidity may not of itself convert the colour former into its coloured form.

An important class of colour formers synthesised by such a route is that of ethenyl phthalides, azaphthalides and diazaphthalides , including the corresponding benzo- compounds i.e. naphtha 1 ides , quinolinides and benzo- pyrazinides, and the corresponding bis-lactone derivatives e.g. of pyro ellitic dianhydride, pyridinetetracarboxylic acid dianhydride and pyr a z inete t r acarboxy 1 i c acid dianhydride. Such colour formers are valuable because their coloured forms exhibit electronic absorption peaks extending into the near infra-red. Images made from such coloured forms can be "read" by optical character recognition equipment. An example of such compounds is 3 , 3-bis [ 2 , 2-bis (4-dimethylaminophenyl ) ethenyl ]-4 ,5 ,6 ,7-tetrachlorophthalide (I) below:

This compound I, along with many others of its class including compounds in which the aromatic ring of a phthalide or azaphthalide is joined to one or more further aromatic rings, is known. It is for example the title compound of Example 2 of U.K. Patent Specification No. 1 496 296. Other Patent Specifications relating to such compounds are U.K. 1 496 297 and 1 492 913 (Appleton Papers Inc.) and U.S. 4 580 153 and European 0 062 544A and 0 127 203A (to Kanzaki Paper) , to which reference may be made.

With this class of compound, and with Compound I specifically, difficulty has been found with highly-coloured by-products as well as with the acidic or potentially acidic residues in the finished product, which is a solid separated from the reaction mixture by, for example, centrifuging. The by-products need to be removed and residues neutralised or washed out, but simple aqueous washing procedures have for example not proved successful in giving a product that is satisfactory when subjected to the usual encapsulation process.

The reasons for coloration problems when found are not clearly known, but in typical encapsulation processes the pR of the aqueous phase is reduced e.g. from about 9.5 to about 4, and this acidic pH appears to increase the level of coloration shown in the product if it is not in purified form initially.

We have now found that as a class lactone colour formers prepared by dehydration condensation, generally with separation of a solid product in the reaction medium, and in particular dehydration condensation products of a substituted ethylene and a phthalic or azaphthalic anhydride (in which we include compounds with the aromatic ring of the phthalide or azaphthalide joined to a further aromatic ring or rings), washed in an alkaline, preferably ammoniacal, polar organic solvent which is preferably methanol or other lower aliphatic alcohol, with removal of acid or potentially acid materials, for example residual acetic anhydride or acetic acid, and of coloured by-products where present.

The method of the invention is particularly applicable in the synthesis of colour forming compounds of the formula (I):

where the ring E has one of the formulae (II), especially (Ha):

₇ where R is a halogen, especially chlorine, atom, an alkyl or alkoxy, especially C-^ to C₄ , group, an aryl, especially phenyl , group or a dialkyl (especially C-^ to C₄ ) a ino group; and m is 0 or an integer from 1 to 4, in particular E is a 3,4,5,6-tetrachloro -1,2-phenylene group: A is an ethylene group of the formula (III):

where one of R and R is a group of the formula (IV):

where each R and R is independently an alkyl, especially C-> to CΠ alkyl, group optionally substituted with an alkoxy or alkoxy alkyl group, especially where the alkoxy residues are C^ to C^ residues, an aralkyl, especially benzyl group, or aryl, especially phenyl,optionally alkyl, e.g. methyl, substituted, group; or

R and R⁵ together with the nitrogen atom to which they are attached form a 5 to 6 embered heterocyclic ring which may include a further hetero-, especially nitrogen or oxygen atom e.g. a pyrollidino- , piperidino- , morpholino-, piperazino- or piperolino-, group; and R⁶ is a hydrogen or halogen atom or an alkyl or alkoxy, especially C-^ to Cg, group; or the group (IV) is a kaioryl or julolidinyl group; the other of 1 and R2 is a group of the formula (IV) as defined above or is a hydrogen or halogen atom or an alkyl, especially C-^ to C₄ alkyl group or an aryl, especially phenyl group which may be substituted by one or more halogen atoms or alkyl or alkoxy, especially C^ to C₄ groups; and R³ is a hydrogen or halogen atom, an alkyl, especially C-^ to ^c i group or an aryl, especially phenyl, group;. B is a group of the formula (III) or formula (IV) as defined above or is an aryl, especially phenyl, group which may be substituted with one or more halogen atoms or alkyl or alkoxy, especially C-^ to C₄ , groups.

When B is not an ethylene group i.e. when the colour former is not di-vinyl , the overall reaction is notionally:

AH + BH + anhydride lactone + H₂0.

In practice it will be more usual to react BH with the anhydride to give an intermediate keto-acid e.g.

(for B =

(and A = phthalic V« (Me)₂) anhydride

(typically under Friedel Crafts conditions

and then dehydration condensing this with the ethylene:-

The washing may be after simple physical separation of a solid product from the reaction medium e.g. by centrifuging or suction filtering, optionally at least partly to convert back to the colourless lactone form any of the colour former in which the lactone ring has opened. It is a substantial advantage to be able to purify the product of the synthesis directly in this way rather than for example following a process of quenching of the mixture into water or ice, alkali treatment and solvent extraction.

The polar solvent for the alkaline agent is of course chosen having primary regard to the (low) solubility properties of the colour former product, methanol being particularly suitable, especially for Compound I. Indeed generally methanol is a poor solvent for lactone colour formers. Methanol has the further advantage that it is a good solvent for the coloured impurities previously referred to, particularly those sometimes present in Compound I as separated from the reaction medium.

It is also desirable for the solvent to take up the (potentially) acidic dehydrating agent, in particular acetic anhydride. Water for example is not satisfactory in this respect as acetic anhydride dissolves primarily by slow two phase .-aqueous hydrolysis to acetic acid rather than as the anhydride.

The alkaline agent, besides neutralising the acidity in the product, also prevents any deleterious effect of the acidity of technical grade methanol where that is the solvent. It further gives practical benefits of not having to handle a product cake impregnated with acetic anhydride/acetic acid in centrifuging and drying to give the product, and of giving a free flowing product. It is preferably ammonia as this is removed easily on drying and is readily soluble in the organic solvents, particularly methanol.

Other alkaline agents are not excluded but are less preferred than ammonia. For example alkalis giving non¬ volatile salts are not preferred because the resulting acetate salts will not be soluble in carbonless solvents and will give a solid residue making handling difficult. Also, in respect of carbonless the acetate salts will tend to buffer the aqueous phase during encapsulation thus making the necessary pH shifts less easy. Volatile alkalis apart from ammonia include low molecular weight amines and alkanolamines_r though they are relatively uneconomic and difficult to use.

The invention is illustrated in the following exemplary embodiment.

EXAMPLE

A mixture of 21 kg of tetrachlorophthalic anhydride and 44 kg of 1 ,l-bis(4-dimethylaminophenyl ) ethylene was heated in 200 kg of acetic anhydride at 80 to 85°C for 4 hours. The reaction mixture was cooled and centrifuged to recover crude product in the centrifuge as a dark blue-green crystalline solid (about 35 to 45 kg wet weight) . This crude product was washed in the centrifuge with a mixture of 40 kg of technical grade methanol and 6 kg of concentrated aqueous ammonia solution (0.89 specific gravity). The washing reaction was appreciably exothermic and the methanolic ammonia solution was recycled until the neutralization was complete. The effluent methanolic solution was coloured dark blue-green. The solid product in the centrifuge was further washed using methanol followed by acetone to remove further blue-green coloured impurities. After drying, about 30 kg (about 57% theory) of 3, 3-bis[2,2-bis(4-dimethylaminophenyl)ethenyl ]-4,5 ,6,7- tetrachlorophthalide was obtained as yellow crystalline solid (the colour of pure Compound I). By comparison the product obtained without the alkaline wash step was a dark green crystalline solid. On test as an encapsulated colour former, the product was found to be much less sensitive to reductions in pH during encapsulation than the product obtained without the alkaline wash step.

Claims

1. Method for the preparation of a lactone colour former by reacting a substituted ethylene with a cyclic aromatic carboxylic anhydride or an intermediate keto acid derived from prior reaction between the anhydride and an aromatic compound, in the presence of a dehydrating agent, wherein following the reaction the solid reaction product formed is separated and washed in an alkaline polar organic solvent with removal of acid or potentially acid materials and of coloured by products where present.

2. Method according to claim 1 wherein the reactants are an aminophenyl substituted ethylene and a phthalic or azaphthalic anhydride as such or with the phthalide or azaphthalide ring joined to a further aromatic ring or rings.

3. Method according to claim 1 or 2 wherein the washing at least partly converts back, to the colourless lactone form, colour former in which the lactone ring has opened.

4. Method according to any preceding claim, wherein the alkaline solvent is ammoniacal.

5. Method according to any preceding claim, wherein the solvent is methanol or other C^to C^ aliphatic alcohol.

6. Method according to any preceding claim, wherein the dehydrating agent itself is or gives rise to the acid or potentially acid materials removed in the washing.

7. Method according to any preceding claim, wherein the dehydrating agent is acetic anhydride.