Free radical meleation of soybean oil via a single‐step process

Abstract

In this study a new value-added product was developed from soybean oil for use as a chemical feedstock. The investigation and optimization of this work resulted in a fast and simple process to maleate soybean oil. An anhydride functionality was introduced into soybean oil through a free radical-initiated maleation. Two initiators were evaluated, 2,5-bis(tertbutylperoxy)-2,5-dimethylhexane peroxide and di-tert-butyl peroxide. The effects of reaction time, initiator concentration, maleic anhydride concentration, and reaction temperature were investigated. The maleated soybean oil was characterized using acid value, iodine value, and FTIR spectroscopy. The acid value was directly related to the initial concentration of maleic anhydride, whereas the concentration and type of initiator had little effect on the acid value. The peroxide-initiated functionalization of soybean oil with maleic anhydride in a closed vessel at elevated pressure and temperature was found to proceed by a Diels-Alder mechanism.Paper no. J10942 in JAOCS 82, 189-194 (March 2005). KEY WORDS:Free radical initiation, maleation, maleic anhydride, process, soybean oil.As the demand for petroleum exceeds production, alternative feedstocks must be found. Agriculturally based chemicals are one of the most attractive alternatives because they are environmentally friendly chemical feedstocks and offer a sustainable source of development. In previous work, we have reported on the rationale, design, and engineering of biobased materials (1,2). One potential agricultural feedstock is soybean oil (SO), which is a mixture of TG containing long-chain FA. Typically, SO contains 4.3-4.6 double bonds per mole depending on the origin of the seed. The presence of unsaturation allows for chemical modifications through specific reactions with these double bonds and the introduction of reactive carbonyl functional groups. There is a great deal of literature on the functionalization of vegetable oils using maleic anhydride (MA) to enhance their reactivity. Morrel and Samuels (3) studied the reaction between MA and conjugated oil systems using oils from china wood and oiticica containing FA with conjugated double bonds. The reaction was found to follow a typical Diels-Alder addition. Root (4) investigated the functionalization of SO with MA and described the use of benzoyl peroxide in the maleation reaction.He concluded that the use of benzoyl peroxide as a catalyst was advantageous, as it allowed the reaction to proceed at a lower reaction temperature of 110°C as compared with 160-190°C when benzoyl peroxide was not used. Root hypothesized that the presence of a peroxide leads to electron delocalization, resulting in conjugation of the double bonds within the unsaturated FA in the SO to form a conjugated system, as shown in Figure 1. However, the mechanism of MA addition to SO and the products of this reaction are still ill defined and are the subject of a great deal of debate in the literature. Clocker (5) postulated a cyclobutane structure for oleic acid adducts. Bickf...

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