The present invention relates generally to alkenyl succinic anhydrides or acids and in particular to a process for their production, their conversion into derivatives and the use of the derivatives in lubricating oil compositions.

The reaction of maleic anhydride or maleic acid with a mono- olefin polymer to produce a polyalkenyl succinic anhydride or acid is well-known. Thus polyisobutene mono (succinic anhydride ⁾ , hereinafter to be referred.to as PIBSA, which is extensively used in the form of its ester or imide as a dispersant in lubricating oil applications, is produced by reacting polysiobutene with ^" maleic anhydride. The reaction may be represented by the following equation:

CH , polyisobutene maleic PIBSA anhydride

It is also known from USP 4012438 that there can be produced alkyl or cycloalkyl tetracarbox lic acid compounds of the formula:

wherein A and C are monovalent succinic acid groups having attachment to B at either of the two carbon atoms of A or C having unsatisfied valences and a hydrogen atom attached to the other unsatisfied carbon atom; and wherein B is a connecting alkane or cycloalkane group of 4 to 30 carbon atoms having 2 of the above-described monovalent groups A and C, which may be the same or different, attached at carbon atoms 1 and 2 or at carbon atoms 1 and 3, and optionally having carbon atom 1 and carbon atom 4 connected by a 1-8 carbon methylene bridge; the remainder of the unsatisfied carbon valences of said bivalent hydrocarbon group being attached to hydrogen atoms; and wherein R is H and

2 3

R and R are H or the same or different hydrocarbyl groups; X and

Y together are -0- or X and Y are the same .or different groups having the structure: -OR, in which R is H or the same or different alkyl or cycloalkyl groups having from 1 to 8 carbon atoms each. The alkyl or cycloalkyl tetracarboxylic acid compound of the a oresaid formula is produced by hydrogenation of the corresponding compound in which B is an alkenyl group of 4 to 30 carbon atcros.

Theoretically it should be possible to produce a polyalkenyl bis (succinic acid or anhydride) , hereinafter re erred to as PABSA, by reacting the mono (succinic acid or anhydride) , as produced by the reaction of maleic anhydride and PIBSA, with further maleic anhydride, as represented by the following equation:-

polyisobutene mono (succinic anhydride) maleic anhydride

polyisobutene bis (succinic anhydride)

OMFI

This has now been achieved by modifying the process conditions or by employing a nickel salt as catalyst or by a combination of both, as described in our copending UK application No. (BP Case No:

4997). A problem commonly encountered in the production of alkenyl succinic anhydrides or acids is the formation of resins by side reactions involving maleic anhydride. It is believed that the acryloyl biradical, formed by elimination of carbon dioxide from maleic anhydride, initiates biradical polymerisation of maleic anhydride to produce a high molecular weight resin.

Up to 20% or more by weight of the maleic anhydride in the initial reaction mixture can be converted to resin under typical conditions used for this reaction. This represents an economic loss to the process, not only in terms of wastage of reactant to unwanted by-product, but also in terms of process costs involved in separating the resin from the product, since in the majority of applications for alkenyl succinic emhydrides the presence of resin is undesirable. For example PIBSA in which the poly- isobutenyl group has a mean average molecular weight of about 1000 is converted by reaction with a polyethylene polyamine into a succinimide which is widely used as a dispersant in lubricating oil formulations. The molecular weight of the PIBSA is so-chosen that the corresponding succinimide is oil soluble. The succinimide produced from resin- containing PIBSA contains an oil insoluble portion arising from the by-product resin. Clearly then it would be desirable to reduce the amount of resin co-produced with PIBSA. Since the resin is believed to be formed by radical polymerisation conventional antioxidants have been employed in the process in an attempt to inhibit the polymerisation. These have not been particularly successful.

We have now found that metallic copper and copper compounds are effective in reducing the amount of resin formed during the production of alkenyl succinic anhydrides and acids.

Accordingly the present invention provides a process for the production of an alkenyl succinic anhydride or acid which process comprises reacting at elevated temperature an olefinic hydrocarbon having at least four carbon atoms with maleic anhydride or maleic

acid in the presence of a resin forming inhibitor comprising metallic copper or a copper compound.

Suitably the elevated temperature may be greater than 150°C and is preferably in the range from 200 to 260°C. Even more preferably the reaction is carried out with a programmed temperature increase over the temperature range 230 to 250°C.

The process may be operated at atmospheric, subatmospheric or superatmospheric pressure. It is preferred to operate at subatmospheric pressure in order to facilitate the removal of volatile impurities. Alternatively, and more preferred, volatile impurities may be removed by operating at super atmospheric pressure whilst sparging the reaction mixture with an inert gas. Preferably the inert gas is nitrogen.

The olefinic hydrocarbon may be linear or cyclic in nature. The olefinic unsaturation may be terminal, as in the case of alpha- olefins, or internal, as in the case of beta, gamma and other such olefins. Examples of suitable linear straight-chain and branched-chain ole ins include 1-butene, 2-butene, 3-hexene, 2-octene, 2,2,4-trimethyl- pentene-3, diisobutylene, 4-methyloctene-l, 7-dodecene, 8-eicosene and 1-triacetene. Examples of suitable cycloaliphatic olefinic hydrocarbons include cyclopentene, cyclohexene, 4-methylcyclopentene and l-methyl-4-ethylcyclohexene. Alternatively the olefinic hydrocarbon may be an olefin polymer which may be a horaopolymer or a copolymer. Suitable olefins include ethylene, propylene and the butylenes. Preferably the olefinic hydrocarbon is polyisobutene. A preferred polyisobutene is polyisobutene of mean average molecular weight (i.e. the average molecular weight for 1 mole of olefin as determined by measurement of the bromine number) in the range 500 to 2000 preferably about 1000. The olefinic hydrocarbon may be reacted with the maleic acid or maleic anhydride in a molar ratio in the range 1:10 to 10:1, preferably in the range 1:1 to 1:3. At molar ratios of 1:1 or less the product of reacting polyisobutene with maleic anhydride or maleic acid will be PIBSA. At molar ratios greater than 1:1 the product can comprise a mixture. of PIBSA and PABSA, particularly - when a nickel salt is employed as catalyst. It is preferred, when molar

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ratios greater than 1:1 are employed to add the maleic acid or anhydride in two or more portions at intervals during the course of the reaction.

The resin forming inhibitor is copper or a copper compound. Copper in the metallic form is preferably used in a finely divided condition. However it is preferred to use a copper compound.

Particularly suitable copper compounds are the copper halides, of which copper iodide is preferred. The amount of copper or copper compound added may suitably be in the range 0.0001 to 1%, preferably 0.001 to 0.1%, expressed in terms of % by weight of elemental copper based on the total weight of the reactants.

Reaction times will vary depending upon the nature of the olefinic hydrocarbon. Generally reaction times may be in the range from about 2 to about 8 hours. It is preferred to avoid protracted reaction times for optimum yields of desired products.

For those applications requiring pure material the alkenyl succinic anhydrides or acids produced according to the invention may be purified by such methods as, for example, fractional distillation, solvent extraction, and decantation. Low molecular weight alkenyl succinic acids or anhydrides, i.e. those containing from 4 to 30 carbon atoms in the alkenyl group may be used as plasticisers for polyvinyl chloride plastic compositions after hydrogenation of the alkenyl group to the corresponding alkyl group and, optionally, conversion of the acid or anhydride groups to ester groups by reaction with C to C _Q alcohols.

1 o

High molecular weight alkenyl succinic acids or anhydrides, i.e. those in which the alkenyl group is derived from an olefin polymer having a mean average molecular weight in the range 500 to

2000 and in particular those derived from a polyisobutene having a mean average molecular weight of about 1000 as prepared by the process of the invention, may be converted to the succinimide by reaction with an amine of the formula:

1 in which x is an integer and R is a C to C alkyl radical or

hydrogen by, for example, the process described in British Patent Specification No: 922831. The succinimide so-produced may be used as a dispersant in lubricating oil compositions. Alternatively the alkenyl succinic anhydride or acid may be converted to an ester by reaction with an alcohol and the ester used as a dispersant in lubricating oil compositions.

The invention will now be illustrated by reference to the following

Examples and Comparison Tests. Example 1 Polyisobutene (400 g of Mn 1000) maleic anhydride (63 g) and cuprous chloride (0.46 g) were added to a stainless steel Magnedrive autoclave (11 capacity) and the mixture was heated for four hours under stirring at 238°C under an applied pressure of 75 psig of nitrogen. The reaction mixture was also sparged continuously with nitrogen using a flow rate of ca. 3 1 h ^" . The reaction product was filtered and the residue, after washing with naphtha to remove residual PIBSA and oven drying at 100°C to constant weight, weighed 0.4 g which was equivalent to ca. 1% molar loss of maleic anhydride fed to resin. The filtrate gave a PIBSA number of 88 mg. KOH equiv. g after correcting for the residual maleic anhydride present (viz. 1.5% w/w).. The PIBSA number is the number of milligrams of potassium hydroxide required to neutralise one gram of sample. Comparison Test 1

Example 1 was repeated but omitting the addition of cuprous chloride the amount of byproduct resin produced amounted to 7.9 g, which corresponded to 16% molar loss of maleic anhydride fed to resin. The filtered reaction product gave a PIBSA number of 90 mg KOH equiv. g after correcting for its maleic anhydride content (viz. 4-6% w/w). Example 2

Polyisobutene (400 g of Mn 1,000) and maleic anhydride (63 g) were added to a stainless steel Magnedrive autoclave 0- 1 capacity) lined

2 with copper Knitmesh, of surface area 8 ft. , and the mixture was heated to 230°C under stirring and an applied pressure of 30 psig of nitrogen. The mixture was heated from 230°C to 240°C over two hours, then for a

further two hours at 240° to 250°C while adding a further amount of maleic anhydride (32 g) and finally for a further four hours at 250° to 260°C.

The resin by-product was separated from the maleinisation product as described in Example 1 above. The amount of resin isolated

(14.6 g) corresponded to a yield loss of 19.8% of the maleic anhydride fed. The filtered reaction product gave a PIBSA number of 124 mg. KCH equiv. g~ after correcting for its maleic anhydride content (viz. 1.3% w/w). Comparison Test 2

Example 2 was repeated omitting the addition of copper Knitmesh and reducing the peak reaction temperature from 260° - 250°C the amount of by-product resin increased to 35 g which corresponded to a yield loss of 45% of the maleic anhydride fed. The filtered reaction product gave a PIBSA number of 102 mg KOH equiv. g after correcting for its maleic anhydride content (viz. 0.5% w/w).

Comparison Tests 1 and 2 are included for purposes of comparison only, and are not processes according to the present invention.