Abstract: Arylacetic acids and their esters, of the formula Ar(CH.sub.2 -COOR).sub.n (where Ar=aryl, R is H or a hydrocarbon radical, and n is 1 or 2) are manufactured by carbonylation of halomethylaryl compounds Ar(CH.sub.2 C).sub.n (where X is Cl, Br or I) with carbon monoxide and a catalyst m.sup.+ ?Fe(O).sub.3 NO!.sup.- (where M is an alkali metal, ammonium or one equivalent of an alkaline earth metal) in the presence of stoichiometric amounts of an inorganic base or of an alcoholate of an alcohol ROH.

Abstract: Pent-4-en-1-al is manufactured by passing an acetaldehyde-acetal of the general formula ##STR1## where R is allyl or alkyl of 1 to 3 carbon atoms, in the gas phase and at from 350.degree. to 450.degree. C, over an active-surface catalyst.

Abstract: Regeneration and separation of catalysts Me(CO)(PR.sub.3).sub.2 Hal(I) and HMe(CO)(PR.sub.3).sub.3 (II), where Me is rhodium or iridium, Hal is halogen and R denotes the same or different hydrocarbon radicals, from distillation residues of hydroformylation mixtures by treating said residues with aqueous acids and peroxides, mixing the resulting Me salt solutions with water-soluble organic solvents and with a phosphine PR.sub.3 and, in the case of the preparation of compound I, with a hydrohalic acid or an alkali metal halide, reacting the solutions at from 0.degree. to 150.degree. C. and from 1 to 250 bars in case I with carbon monoxide or compounds eliminating carbon monoxide and in case II additionally with hydrogen, and separating the resulting compound I or II.