Synthesis of Alpha Olefins: Catalytic Decarbonylation of Carboxylic Acids and Vegetable Oil Deodorizer Distillate (VODD)

Hang Wai Lee ,Ka Fu Yung

doi:10.3390/catal11080876

Abstract

Decarbonylation of carboxylic acids provides an effective protocol for producing alpha olefins; however, previous literature has focused on the palladium-bisphosphine catalysts and has only sporadically studied the palladium-monophosphine catalyst. To investigate the catalytic activity of the palladium-monophosphine catalyst on decarbonylation of carboxylic acids, new monophosphine ligands were synthesized (NP-1, NP-2, CP-1 and CP-2). By employing (1–3 mol%) palladium-naphthylphosphine catalysts, various carboxylic acids were converted into corresponding alpha alkenes with good yields and selectivity within a short period of time. Vegetable oil deodorizer distillate (VODD), which is a by-product from the vegetable oil refinery process, was found to be rich in free fatty acids and there is great interest in turning vegetable oil deodorizer distillate into value-added compounds. It is noteworthy that our catalytic system could be applied to convert vegetable oil deodorizer distillate (VODD) into diesel-like hydrocarbons in a good yield.

Highlights

Owing to the depletion of fossil fuels, there is a growing demand for the exploration of alternative renewable energy sources [1,2,3,4]
Extensive studies that focused on the development of heterogeneous catalytic decarbonylation/decarboxylation reactions were carried out, and TiO [5,6,7,8,9], Pd/C [10,11,12,13,14,15], Pd/Al2O3 [16,17], Pt/Al2O3 [18,19,20], Ni/SiO2 [15], Ru/C [15], Rh/C [15], Os/C [15], and WOx-Al2O3 [21] were found to convert fatty acids into alkanes and alkenes in response to harsh reaction conditions (>300 ◦C) [2]
Amines are crucial for stabilizing palladium-active species and help to enhance selectivity of the reaction [25], different amines were tested (Table 1, entries 10–13)

Summary

Introduction

Owing to the depletion of fossil fuels, there is a growing demand for the exploration of alternative renewable energy sources [1,2,3,4]. Biomass-derived hydrocarbons (diesel-like hydrocarbons) are believed to be a good alternative for fossil fuels since they could be readily obtained by cracking or decarbonylation/decarboxylation of a biomass such as vegetable oils. Decarbonylation/decarboxylation of biomass-derived carboxylic acids is attractive since substrates are inexpensive and are readily available from various natural sources [1], and highly selective alkenes can be obtained. Palladium, in conjunction with strong coordination bisphosphine ligands ( biaryl ether ligands, DPEPhos, or XantPhos), were proven to be an effective catalyst in decarbonylation reactions to afford alkenes with good alpha-selectivity [38]. Jensen et al reported the benefit of hemilabile POP-type ligand (e.g., DPEPhos) in the deoxygenation of fatty acids reaction [39].

Results and Discussion

General Procedures for the Pd-Catalyzed Decarbonylation of Carboxylic Acids

General Procedures for the Synthesis of NP Ligands

Conclusions