Hydroformylation process

1. A process to produce 4-hydroxybutyraldehyde comprising reacting allyl alcohol with carbon monoxide and hydrogen in the presence of a solvent and a catalyst system comprising a rhodium complex and a 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis[bis(3,5-di-n-alkylphenyl)phosphino]butane.

2. The process of claim 1 wherein the catalyst system comprises the rhodium complex and 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis[bis(3,5-dimethylphenyl)phosphino]butane.

3. The process of claim 1 wherein the catalyst system comprises the rhodium complex and 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis[bis(3,5-diethylphenyl)phosphino]butane.

4. The process of claim 1 wherein the solvent is selected from the group consisting of C 5 –C 20 aliphatic hydrocarbons, C 6 –C 12 aromatic hydrocarbons, ethers, alcohols, and mixtures thereof.

5. The process of claim 1 wherein the solvent is selected from the group consisting of toluene, cyclohexane, methyl t-butyl ether, and mixtures thereof.

6. The process of claim 1 wherein the rhodium complex comprises rhodium and ligands selected from the group consisting of hydride, carbonyl, trialkyl or triaryl phosphines, diphosphines, cyclopentadienyls, 2,4-alkanedionates, and mixtures thereof.

7. The process of claim 1 wherein the reaction is performed at a temperature within the range of about 45° C. to about 85° C. and a pressure within the range of about 30 to about 400 psig.

8. The process of claim 1 wherein the catalyst system also comprises a monophosphine compound.

9. The process of claim 8 wherein the monophosphine compound is triphenylphosphine.

10. The process of claim 1 wherein the concentration of carbon monoxide in the liquid phase is maintained above 4 mmols/liter.

11. The process of claim 1 further comprising hydrogenating the 4-hydroxybutyraldehyde in the presence of a hydrogenation catalyst to form 1,4-butanediol.

12. The process of claim 11 wherein the hydrogenation catalyst is a nickel catalyst.