**1. Introduction**

Butadiene-1,3 (BD) is diolefin containing two conjugated double bonds. In oxidation, BD exhibits properties inherent to all olefins, but higher reactivity was compared to but-1-ene and

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but-2-ene. Both BD and C4 -olefins can be a feedstock for producing valuable chemicals by gasphase oxidation [1, 2]. The oxidation on oxide catalysts in gas phase results in the formation of maleic anhydride together with crotonaldehyde and 2,5-dihydrofuran. Centy and Trifiro suggested a simple consecutive pathway for BD oxidation over V-P-oxide catalysts [3, 4], whereas Honicke et al. proposed multiple pathways from BD to crotonaldehyde, 2,5-dihydrofuran, 2-butene-1,4-dial, 2(5H)-furanone and furan, and finally to maleic anhydride over V2 O5 catalysts [5]. Schroeder specified the oxidation pathway on V-Mo-oxide catalysts, including 3,4-epoxy-1-butene as a primary oxidation product [6]. Epoxidation of BD occurs over Ag catalysts [7–10] used in industry for the production of ethylene oxide and intensively investigated in the oxidation of other olefins (e.g., [11, 12]). 3,4-Epoxy-1-butene is further converted into 2,3-dihydrofuran followed by hydrolysis to form 4-hydroxybutyraldehyde. The secondary transformations occur directly under epoxidation conditions on Ag catalysts promoted with B-P [13], Mo [14], and Mo-P-Sb [15] or by subsequent treatments of 3,4-epoxy-1-butene.

one of the double bonds of BD is involved in the oxidation. Neat or dissolved in a nonpolar solvent, BD interacts with oxygen at moderate temperature according to radical chain

Reactivity of a Simplest Conjugated Diolefin in Liquid-Phase Oxidation: Mechanisms and Products

erated by increasing the temperature or adding free radical initiators and inhibited by adding acids. From the NMR analysis, molecular structure of the polyperoxide formed at 50°C in the presence of 37 Torr of oxygen was composed of equal amounts of 1,4- and 1,2-butadiene units separated by peroxide units [31]. The structure of the polyperoxide (the ratio of 1,4- to 1,2-butadiene units) does not depend on the reaction temperature, whereas the content of bound oxygen in the polyperoxide varies with oxygen pressure. The ratio of peroxide to hydrocarbon units is below 1 at a low oxygen partial pressure. Thermal decomposition as well as hydrogenation of polyperoxide leads to the formation of 3-butene-1,2-diol and 2-butene-1,4-diol or corresponding saturated diols, preferably

Decomposition of the polyperoxide forms not only 3-butene-1,2-diol and 2-butene-1,4-diol but also side products such as formaldehyde, acrolein (from 1,2-units), and resinous insoluble material (presumably resulting from the reaction of the 1,4-units with aldehydes) [31]. Therefore, the preferred formation of 1,4-oxygenates from the thermal decomposition of polyperoxide is

The rate of decomposition of the polyperoxide increases with increasing temperature, addition of bases (amines) [36], or metal ions as radical initiators. Butadienyl polyperoxide is readily decomposed in the presence of metal ions of variable oxidation state. Therefore, the transition metal compounds participate as catalysts in the radical chain oxidation of BD with oxygen. The oxidation products are similar to those obtained under the decomposition of the polyperoxide. 3-Butene-1,2-diol and 2-butene-1,4-diol can be obtained with the selectivity sufficiently high for the chain radical process, especially if one considers the low stability of these products with respect to secondary oxidation. Thus, a mixture of 3-butene-1,2-diol and 2-butene-1,4-diol has been prepared by oxidative dihydroxylation of BD with oxygen in acetic

We tested Pd and Au catalysts in the radical chain oxidation of BD in polar media. Both soluble palladium acetate and insoluble supported metals caused the formation of the products,

not a strong support of predominance of 1,4-units in the polyperoxide structure.

H6 O2

. From a practical point of view, the most valuable 2-butene-1,4-diol

[30]. The reaction is accel-

101

http://dx.doi.org/10.5772/intechopen.71259

mechanism to form oligomeric butadiene polyperoxide, C4

1,4-derivatives (**Scheme 1**) [30, 32–35].

acid solution of Pd(OAc)2

has been formed with selectivity of 25% [37].

**Scheme 1.** Formation and reductive decomposition of the polyperoxide [30].

In the early 1980s, oxidation of n-butane has become the preferred method for manufacturing maleic anhydride [16, 17]. The invented synthesis of maleic anhydride from butane creates a competition for the gas-phase oxidation of BD since hydrogenation of maleic anhydride opens a possibility of producing various oxygenates, which produced from BD earlier. At the same time, the gas-phase oxidation of BD still suffers from formation of polymer resins, which leads to excessive consumption of raw materials and catalyst deactivation. This problem and large power consumption inherent to all gas-phase reactions are absent in the liquidphase oxidation since the low temperature and application of appropriate solvents prevent the formation of the resins. The liquid-phase low-temperature oxidative reactions, in particular the oxidation of olefins, were intensively studied at the end of the last century [18–23]. A renewed interest in this area is growing now [24–27] and can be expected to be strengthened in the nearest future as a response to modern requirements of green chemistry to minimize power and materials consumption. In addition, the liquid-phase reactions are well applicable for the oxidation of various olefins and BD because of high reactivity of these hydrocarbons that allows the oxidation at low temperature. At the same time, BD becomes more affordable owing to permanent improvements in its manufacturing.

The title of this chapter concerns the application of green oxygen (air and hydrogen peroxide) in liquid-phase conditions. The liquid-phase oxidative reactions are an important part in chemistry of all olefins and, in particular, of the simplest representative of conjugated diolefins as they open many routes for the conversion of the hydrocarbons. We represent here an analysis of literature information concerning the oxidation of BD in liquids and references to the related reactions of olefins. In detail, we described the catalytic systems in the study of which we acquired our own experience.
