Hydroformylation of mono-.alpha.-olefins and mono-.alpha.-acetylenes

A hydroformylation process comprising reacting hydrogen and carbon monoxide with a mono-.alpha.-olefinically or mono-.alpha.-acetylenically unsaturated aliphatic hydrocarbon, said process being carried out at a temperature in the range of 50.degree. -150.degree. C at a pressure of 5 to 100 atmospheres and in the presence of a liquid reaction medium having dissolved therein a catalytic quantity of a catalyst having the formula L.sub.n M.sup.v X.sub.y, wherein L is a ligand molecule having a donor atom selected from the class consisting of phosphorus and arsenic, said donor atom having a pair of electrons available for donation to metal atom M;

• n is the number of ligand molecules present and is a positive integer having a value of at least one and less than 4;
• M is a metal atom selected from the class consisting of ruthenium, osmium, rhodium, iridium, palladium and platinum, v is the valency state of said metal atom and is a positive integer having a value of from 1 to 4;
• X is a halogenoid moiety selected from the class consisting of halogen, cyanide, cyanate and thiocyanate;
• Y is the number of halogenoid moieties present and is an integer having a value of from 1 to 3.