Addition reactions between a compound containing an active hydrogen atom and a compound containing an unsaturated linkage both as defined below are effected in the presence as catalyst of a mixture of an alkali metal and iron. The compound with an active hydrogen atom may be : (1) A carbocyclic or heterocyclic compound having attached to a nuclear, unsaturated carbon atom a hydrogen-bearing atom of a hydrocarbon group. The ring may be aromatic or hydro-aromatic or both, fused or unfused, and suitable heterocyclic rings are pyridine, furan, thiophene, pyrrola, pyrazole, indole or carbazole. The hydrocarbon substituent may be unsaturated but is preferably saturated, straight or branched, chain or cyclic and may be substituted by an aryl group. The nucleus may be substituted by chlorine, methoxy, ethoxy or nitro groups ; hydro-aromatic compounds preferably contain non-geminately disposed substituents. The unsaturated compound attaches itself to the hydrogen-bearing nuclearlybound carbon atom. Many are specified; (2) Unsubstituted aromatic mono- or polycyclic carbo- or herero-cyclic compounds, e.g. benzene, naphthalene, anthracene, pyridine, furan or thiophene ; (3) Acyclic or cyclic compounds with an olefinic double bond, many mono-olefines and cyclo-olefines being specified; (4) Ammonia and primary or secondary aliphatic amines of the formula R1R2NH where R1 and R2 are hydrogen or aliphatic radicals and (5) the corresponding phosphines, R1R2PH, each of which attach the unsaturated compound to the nitrogen or phosphorous atom to form a primary, secondary or tertiary amine, or phosphine. The unsaturated compound may be : (1) A compound having a non-conjugated non-aromatic carbon-tocarbon double bond, many mono- and polyolefines, both cyclic and acyclic, being specified ; (2) A compound containing a non-conjugated carbon-to-oxygen double bond, in which the oxygen-bearing carbon carries no hydrogen, e.g. mono- and di-ketones, cyclic or acyclic ; (3) An unsubstituted carbocyclic aromatic or heterocyclic compound or an alkyl substituted derivative having at least one nuclear hydrogen atom ; the active hydrogen compound adds on to the nucleus. It is preferred to use at least an equimolar amount of the active hydrogen compound as compared to the unsaturated compound. Preferred conditions are 100 DEG C.-350 DEG C. and 5-100 atmospheres. An inert solvent may be present. The iron is preferably in the form of a powder of 20-325 mesh with a surface area about 0,5 m.2/gm. or larger. The weight ratio of iron to alkali metal may be between 1 : 100 and 100 : 1. If desired they may be composited with an inert support. Promoters may be added, e.g. fused ring polycyclic aromatic hydrocarbons, acetylenic hydrocarbons, heterocyclic compounds containing four or five carbons and nitrogen in the ring, alcohols, carboxylic acids, ethers, organic nitrates and cyanides, hydrocarbon halides, and organic peroxy and compounds. The following reactions are exemplified : (1) the addition of ethylene to toluene to give n-propyl benzene and 3-phenyl pentane ; (4) the addition of propylene to toluene to give isobutyl benzene ; (5) the addition of ethylene to 1-methyl-1-cyclohexene to give 1-isobutyl-1-cyclohexane ; (b) the addition of ethylene to cyclohexene to give ethyl cyclohexenes ; (7) the dimerisation of propylene to 4-methyl-1-pentene ; (8) the codimerisation of ethylene and propylene to 1- and 2-pentenes. Specification 740,978 is referred to.ALSO:A catalyst for addition reactions between organic compounds, comprises a mixture of an alkali metal and iron. The activity of the alkali metals rises with rising atomic weight from lithium to cesium. The iron is preferably a powder of 20-325 mesh, though iron turnings can be used. The weight ratio of iron to alkali metal may be from 1:100 to 100:1. The alkali metal is generally liquid under the reaction conditions and the catalyst may be a slurry of iron in the alkali metal, or the iron may be composited with or deposited on an inert support and the alkali metal added to the composite, e.g. as a film. The surface area of the iron may be about 0.5 m.2/gm. Specification 740,978 is referred to.