Process for preparing aldehydes

A process for selectively producing aldehydes which comprises introducing into a reaction zone (1) methanol, (2) carbon monoxide, (3) hydrogen, (4) cobalt, (5) iodine and (6) a ligand containing phosphorus atoms separated by a sterically constrained carbon-carbon bond, the molar ratio of carbon monoxide to hydrogen being in the range of about 2:1 to about 1:2, the molar ratio of cobalt to said ligand being in the range of about 1:2 to about 7:1, the molar ratio of cobalt to iodine being in the range of about 1:1.15 to about 1:15, and the weight percent of combined cobalt and iodine, based on the methanol, being in the range of about 0.01 to about ten percent, and then subjecting said contents to an elevated temperature of about 150.degree. to about 250.degree. C. and an elevated pressure of at least about 2200 pounds per square inch for about five minutes to about five hours, sufficient to convert methanol to a product predominating in aldehydes.