New 2-hydroxyl-3-[1-(1H-imidazol-4-yl)alkyl]-benzenecarboximidamides as well as their salts, having the formula ##STR1## wherein R.sub.1 is hydrogen or an alkyl radical having 1 to 4 carbon atoms, R.sub.2 is hydrogen a hydroxyl group, an amino group or an alkyl radical having 1 to 4 carbon atoms, R.sub.3 is hydrogen, or R.sub.2 and R.sub.3 together are --CH.sub.2 -CH.sub.2 --; processes for the preparation thereof, and ophthalmic compositions comprising the same are also described. These compounds are capable of lowering intraocular pressure and can be used in the prevention and treatment of glaucoma.

A process for the manufacture of N-phenylmaleimide which comprises reacting maleic anhydride with aniline in a single step at elevated temperature in the presence of a water-immiscible organic solvent capable of forming an azeotrope with water and of p-toluenesulfonic acis as catalyst. According to the invention, N-phenylmaleimide recovery comprises the successive steps of: (a) treating the reaction mixture in a dilution and filtration zone, in which it is diluted with an additional amount of the solvent, the diluted mixture being filtered at low temperature in order to separate a solid cake containing the catalyst and impurities, and a liquid filtrate consisting of a solution of N-phenylmaleimide in the solvent, (b) distilling this solution of N-phenylmaleimide under reduced pressure so as to successively separate the solvent and substantially pure N-phenylmaleimide, whereas the distillation residue is treated exactly as indicated in (a) above in a dilution and filtration zone in order to recover the N-phenylmaleimide therefrom, the filtrate being recycled for use in step (a) to dilute the reaction mixture produced by a subsequent synthesis. Furthermore, the filter cakes from steps (a) and (b) are washed with solvent obtained by distillation in step (b) and the resulting wash solvents are recycled for use in the reaction and/or dilution zones. A high purity N-phenylmaleimide is obtained in an overall yield exceeding 86 mole %; the problem of waste water and pollution is reduced to a minimum.

A process for producing gamma-butyrolactone by catalytic hydrogenation of maleic anyhydride in the liquid phase with hydrogen, at a high temperature and under pressure, in the presence of a catalyst comprising nickel and palladium deposited on a support, wherein said support is a silica based support having a very high specific surface area , the value of which may range from 50 m.sup.2 /g, preferably from about 100 m.sup.2 /g to about 800 m.sup.2 /g and more. Very high conversion rates of 90-98 mole % and excellent selectivities to gamma-butyrolactone of 95 to 97 mole % are achieved by the process.