Butyraldehyde plasticizer

The important solvent and plasticizer intermediate, 2-ethylhexanol, is manufactured from -butyraldehyde by aldol addition in an alkaline medium at 80-130°C and 300-1010 kPa (3-10 atm). 

Aldehydes fiad the most widespread use as chemical iatermediates. The production of acetaldehyde, propionaldehyde, and butyraldehyde as precursors of the corresponding alcohols and acids are examples. The aldehydes of low molecular weight are also condensed in an aldol reaction to form derivatives which are important intermediates for the plasticizer industry (see Plasticizers). As mentioned earlier, 2-ethylhexanol, produced from butyraldehyde, is used in the manufacture of di(2-ethylhexyl) phthalate [117-87-7]. Aldehydes are also used as intermediates for the manufacture of solvents (alcohols and ethers), resins, and dyes. Isobutyraldehyde is used as an intermediate for production of primary solvents and mbber antioxidants (see Antioxidaisits). Fatty aldehydes Cg—used in nearly all perfume types and aromas (see Perfumes). Polymers and copolymers of aldehydes exist and are of commercial significance. 

Polyols. Several important polyhydric alcohols or polyols are made from formaldehyde. The principal ones include pentaerythritol, made from acetaldehyde and formaldehyde trimethylolpropane, made from -butyraldehyde and formaldehyde and neopentyl glycol, made from isobutyraldehyde and formaldehyde. These polyols find use in the alkyd resin (qv) and synthetic lubricants markets. Pentaerythritol [115-77-5] is also used to produce rosin/tall oil esters and explosives (pentaerythritol tetranitrate). Trimethylolpropane [77-99-6] is also used in urethane coatings, polyurethane foams, and multiftmctional monomers. Neopentyl glycol [126-30-7] finds use in plastics produced from unsaturated polyester resins and in coatings based on saturated polyesters. 

Di-2-EthylhexylPhthalate. In Western Europe, di-2-ethylhexyl phthalate [117-81-7] (DEHP), also known as dioctyl phthalate (DOP), accounts for about 50% of all plasticizer usage and as such is generally considered as the industry standard. The reason for this is that it is in the mid-range of plasticizer properties. DEHP (or DOP) is the phthalate ester of 2-ethyIhexanol, which is normally manufactured by the dimerization of butyraldehyde (eq. 2), the butyraldehyde itself being synthesized from propylene (see Butyraldehydes). 

Homogeneous rhodium-catalyzed hydroformylation (135,136) of propene to -butyraldehyde (qv) was commercialized in 1976. -Butyraldehyde is a key intermediate in the synthesis of 2-ethyIhexanol, an important plasticizer alcohol. Hydroformylation is carried out at <2 MPa (<290 psi) at 100°C. A large excess of triphenyl phosphine contributes to catalyst life and high selectivity for -butyraldehyde (>10 1) yielding few side products (137). Normally, product separation from the catalyst [Rh(P(C2H2)3)3(CO)H] [17185-29-4] is achieved by distillation. 

The largest commercial process is the hydroformylation of propene, which yields n-butyraldehyde and isobutyraldehyde. n-Butyraldehyde (n-butanal) is either hydrogenated to n-butanol or transformed to 2-ethyl-hexanol via aldol condensation and subsequent hydrogenation. 2-Ethylhexanol is an important plasticizer for polyvinyl chloride. This reaction is noted in Chapter 8. 

Phthalic anhydride s main use is for producing plasticizers by reactions with C4-C10 alcohols. The most important polyvinyl chloride plasticizer is formed by the reaction of 2-ethylhexanol (produced via butyraldehyde. Chapter 8) and phthalic anhydride ... 

Hydroformylation is an important industrial process carried out using rhodium phosphine or cobalt carbonyl catalysts. The major industrial process using the rhodium catalyst is hydroformylation of propene with synthesis gas (potentially obtainable from a renewable resource, see Chapter 6). The product, butyraldehyde, is formed as a mixture of n- and iso- isomers the n-isomer is the most desired product, being used for conversion to butanol via hydrogenation) and 2-ethylhexanol via aldol condensation and hydrogenation). Butanol is a valuable solvent in many surface coating formulations whilst 2-ethylhexanol is widely used in the production of phthalate plasticizers. 

In this chapter we shall review the aqueous hydroformylation of substrates other than simple terminal alkenes. Of course, preparation of butyraldehyde or plasticizer alcohols is also a synthetic application but in the following a few examples are given for application of hydroformylation in reactions of more complex substrates and in synthesis of more elaborate molecules. Most of these chemical transformations could also be effected in one-phase reactions (organic or aqueous), however, the biphasic variants were not inferior in chemistry and offered the advantage of easy catalyst-product separation. 

Ethyl alcohol has been made by the hydration of ethylene (9) since 1930. Like isopropyl alcohol, part of the output is used as a solvent, but most is converted to other oxygenated chemicals. Its most important raw material use is conversion to acetaldehyde by catalytic air oxidation. Acetaldehyde, in turn, is the raw material source of acetic acid, acetic anhydride, pentaerythritol, synthetic n-butyl alcohol (via aldol condensation), butyraldehyde, and other products. Butyraldehyde is the source of butyric acid, polyvinyl butyral resin, and 2-ethylhexanol (octyl alcohol). The last-named eight-carbon alcohol is based on the aldol condensation of butyraldehyde and is used to make the important plasticizer di-2-ethylhexyl phthalate. A few examples of the important reactions of acetaldehyde are as follows ... 

In the presence of dilute sodium or potassium hydroxide, -butyraldehyde undergoes the aldol reaction to form 2-ethyl-3-hydroxyhexanal [496-03-7] which, on continued heating, is converted into 2-ethyl-2-hexenal [26266-68-2]. Hydrogenation of the latter gives 2-ethyl-1-hexanol [104-76-7], a principal plasticizer alcohol. 

The majority (92% in 1988) of the butyraldehyde produced in the United States is converted into 1-butanol and 2-ethylhexanol (2-EH). 2-EH is most widely used as the di(2-ethylhexyl) phthalate [117-81-7] ester for the plasticization of flexible PVC. Other uses for 2-EH include production of intermediates for acrylic surface coatings, diesel fuel, and lube oil additives (24). 

The highest volume oxo chemical in the United States, n-butyraldehyde, is converted mainly into u-butanol, employed chiefly to produce butyl acrylate and methacrylate. In contrast, the principal -butyraldehyde derivative in Europe and Japan is 2-ethylhexanol, the precursor to the polyi vinyl chloride) (PVC) plasticizer, DOP. 

While n-butanol from the oxo process did not become a major intermediate for PVC plasticizers, the development was nonetheless a breakthrough of far-reaching significance. The precursor of n-butanol in the oxo process is n-butyraldehyde. This made possible the manufacture of 2-ethylhexanol by "single aldol" at lower cost than the "double aldol" route via acetaldehyde. 

Another important application of butyraldehyde is in the production of oxo-alcohols for use as plasticizers used to improve mixing of solid compounds that must be molded or extruded into specific shapes. The hydrogenation catalyst is Ni/Al203. 

Each aldehyde can be hydrogenated to the corresponding alcohol for use as a solvent or an intermediate for plasticizers and resins. n-Butyraldehyde is also converted to 2-ethylhexanol by sequential condensation and hydrogenation. 2-Ethylhexanol is used to make the phthalate ester, which finds wide use as a plasticizer of PVC. 

The largest volume hydroformylation reaction converts propylene into n-butyraldehyde, from which is made 1-butanol for solvents, or 2-ethylhexanol (the phthalate ester of which has been widely used as a plasticizer for PVC) via an aldol condensation. Estimated world production of butanol is approaching 2 Mt/a. 

Butanal is used in the manufacture of rubber accelerators, synthetic resins, solvents, and plasticizers. -Butyraldehyde is used as an intermediate in the manufacturing of plasticizers, alcohols, solvents, and polymers (such as 2-ethylhexanol, -butanol, trim-ethylolpropane, -butyric acid, polyvinyl butyral, methyl amyl ketone). It is also used as an intermediate to make pharmaceuticals, agrochemicals, antioxidants, rubber accelerators, textile auxiliaries, perfumery, and flavors. It has no therapeutic use at the present time. 

The most important and oldest application of aqueous biphasic, homogeneous catalysis is hydroformylation (oxo process, Roelen reaction). This process is used to produce n-butyraldehyde, the desired main product of the reaction of propylene, which is converted by aldolization into 2-ethyUiexenal and this is finally hydrogenated to give 2-ethylhexanol (2-EH), the most economically important plasticizer alcohol (Scheme 1) ... 

EH is esterified with phthalic acid to produce the standard plasticizer dioctyl phthalate (DOP). With a capacity of roughly 5 million metric tons per year, n-butyraldehyde is among the most important applications of homogeneous catalysis [9,35]. 

Butyraldehyde is used mainly as an intermediate in the production of synthetic resins, rubber vulcanization accelerators, solvents, and plasticizers. It reacts with polyvinyl alcohol to form polyvinyl butyral which is used as an interlayer for safety glass as well as for coating fabrics. Isobutyraldehyde is used as a solvent or plasticizer in the plastics industry, or as a raw material in the synthesis of isobutyl alcohol, methacrylic acid, neopentyl glycol, etc. 

About 75% of the n-butyraldehyde generated is converted into 2-ethylhexanol, which is almost completely consumed as a phthalate ester, e.g., in plasticizers for PVC. The remainder of the butyraldehydes are either used as such for chemical synthesis, converted to acids or amines, or - more important today - hydrogenated to the butanols which are either directly sold as solvents or are further converted into acrylate esters, glycol ethers, butyl acetate, and butyl amines. 

This figure does not include 2-ethylhexa-nol. n-Butyraldehyde-denved 2-ethylhexa-nol is by far the most important plasticizer alcohol, with an estimated worldwide consumption of 2.4 million t. 

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