With applications ranging from energy production to chemical manufacture, cleavage of carbon-carbon bonds in aldehydes and ketones plays a key role in organic chemistry.
The disconnection of carbon-carbon bonds is important in organic chemistry, and generally even more challenging than the formation of these bonds. The project was organized in two parts. In the first part, the focus was the hydroxide-mediated cleavage of carbon-carbon bonds in aldehydes and ketones. The second part involved Ruthenium catalyzed dehydrodecarbonylation of primary alcohols. Both types of reactions result in carbon-hydrogen bonds in place of carbon-carbon bonds.
Hydroxide-mediated cleavage of carbon-carbon bonds in aldehydes and ketones has been known for more than a century. The generated fragments are the carboxylate and various neutral residues such as ketones, nitroalkanes, sulphonyl alkanes, tri-halo-alkanes, and other moieties. The neutral residues are all weak acids (pKa values between 10 and 40). In the project, toluene residues with a pKa of about 41, was also cleaved from ketones with hydroxide in generally good yields.
Cleavage of different substituted benzylic ketones and aldehydes promoted by hydroxide sources in various solvent systems were studied to investigate the scope of the reaction and clarify the mechanism. Kinetic data from Hammett correlation plots were compared with theoretical values from density functional theory (DFT) calculations. DFT calculations were also conducted to determine the relative free energies of possible intermediates and transition states.
Dehydro-decarbonylation of alcohols is an attractive reaction based on two individual processes: the acceptorless dehydrogenation of an alcohol and the decarbonylation of the resulting aldehyde. In this transformation, valuable products are formed such as the unfunctionalized organic residue and two gases, hydrogen and carbon monoxide, respectively.The gaseous mixture is also known as synthesis gas (“SynGas”) and has many applications ranging from energy production to chemical manufacture.
Rhodium and Iridium complexes have previously been investigated to mediate this process. However, both of these metals have limitations in scope and affordability. Therefore, in this work a cheaper alternative is presented, based on the system Ru(COD)Cl and the phosphine P(o-tolyl)3 for the dehydrogenative decarbonylation of alcohols.
The reaction was applied to both benzylic and long chain linear aliphatic alcohols. The intermediate aldehyde can be observed during the transformation, which is therefore believed to proceed through two catalytic cycles involving first dehydrogenation of the alcohol, followed by decarbonylation of the resulting aldehyde.
Difference between reactions running with a) 10% of ligand and b) 15 %. The first one show catalyst decomposition responsible for the black color, while the second is clear.