Butyraldehyde aldol condensation with

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. 

The n-butyraldehyde is treated with a 2 per cent w/w aqueous sodium hydroxide and undergoes an aldol condensation at a conversion efficiency of 90 per cent. The product of this reaction, 2-ethylhexanal, is separated and then reduced to 2-ethylhexanol by hydrogen in the presence of a Raney nickel catalyst with a 99 per cent conversion rate. In subsequent stages of the process (details of which are not required), 99.8 per cent of the 2-ethylhexanol is recovered at a purity of 99 per cent by weight. 

This substrate was prepared by aldol condensation of tetralone with iso-butyraldehyde in the presence of aqueous sodium hydroxide[9]. 

The order of activity per unit surface area was equal to that in the case of selfcondensation of acetone and in agreement with the order of basicity of the solids, namely, SrO > CaO > MgO. However, the authors found that the rate-determining step for aldol condensation of n-butyraldehyde is the a-hydrogen abstraction by the active sites, which are the surface ions. The differences in rate-determining step and active sites in the condensation of butyraldehyde and aldol condensation of the acetone were attributed to differences in acidity of the a-hydrogen in the two molecules. CaO was slightly more active than MgO at 273 K after a reaction time of 1 h, maximum conversions of 41% were observed with selectivities to 2-ethyl-3-hydroxy-hexanal and to the corresponding Tishchenko reaction product (2-ethyl-3-hydroxy- -hexyl butyrate) of 39.8 and 56.9%, respectively. 

Shu and co-workers (35) identified 2-isobutyl-3,5-diisopropylpyridine, 2-pentyl-3,5-dimethylpyridine, and its dihydro derivative obtained under similar conditions. Sultan (29) confirmed the presence of 3,5-diethyl-2-propylpyridine in a model system consisting of butyraldehyde and ammonium sulfide. Our proposed mechanism of their formation (20) consists of three steps 1) aldol condensation of the starting aldehydes to 2,4-alkadienals, 2) imine formation with ammonia, and 3) subsequent cyclization and oxidation to corresponding pyridines. An alternate mechanism, suggested by Shu and co-workers (33), takes into consideration the isolated dihydro derivatives. Hwang and co-workers described another dihydro derivative (19, R = Bu, R = R" = Pr, R= H) (37). 

Ethylhexanol is usually produced by subsequent aldolization of butyraldehyde produced in the oxo reaction followed by hydrogenation of the intermediate unsaturated aldehyde.89 In Esso s Aldox process, however, in situ aldol condensation is effected by suitable promoters.11 Magnesium ethoxide and soluble zinc compounds are recommended to promote controlled aldolization during the oxo reaction. The Shell variant uses potassium hydroxide. Serious disadvantages (mixed aldolization with the branched aldehyde, problems associated with recycling of the additives), however, prevented wider use of the Aldox process. 

Pd-containing aluminophosphate molecular sieves have been used to carry out crossed aldol condensations between an aldehyde and a ketone by using a 0.5 % Pd/ MnAPSO-31 catalyst in a vapour-phase fixed bed reactor.[14] Thanks to the excess of the ketone with respect to the aldehyde (4 1), it is possible to get high selectivity to the desired product, i.e. 70 % of heptan-2-one from n-butyraldehyde and acetone and 89 % of pentan-2-one from acetaldehyde and acetone, the major by-product being, in both cases, MIBK from acetone self-condensation. 

These silyl enol ethers are probably the best way of carrying out crossed aldol reactions with an aldehyde as the enol partner. An example is the reaction of the enol of the not very enolizable iso-butyraldehyde with the very enolizable 3-phenylpropanal. Mixing the two aldehydes and adding base would of course lead to an orgy of self-condensation and cross-couplings. 

The aldol condensations were carried out with the enolates derived from 3-oxocyclopent-1-ene or 3-oxo-cyclohex-l-ene and benzaldehyde or butyraldehyde (see p. 186, 443). 

Cyclocondensations of simple carbonyl compounds—such as acetone, methyl ethyl ketone, propionaldehyde, or the butyraldehydes—and simple diamines—such as ethylenediamine and 1,2- or 1,3-propanediamine—were studied by Curtis and coworkers in the 1960s (Curtis, 1968). The resulting complexed cyclic bis Schiff base was reduced to form the tetraaza-crown ligand. The cyclic product is a result of an aldol condensation of the carbonyl compound, followed by ring-closure reactions with the diamine. In 1966,... 

Aldol condensations are typical base-catalyzed reactions. The reaction of w-butyraldehyde to 2-ethyl-3-hexanal at 275 °C occurs with 100 % conversion of butyraldehyde and 85 % selectivity [39] (Scheme 14.2). 

Directed aldol condensation. House et al. have published a detailed procedure for the aldol condensation of the lithium enolate of phenylacetone with n-butyraldehyde in the presence of zinc chloride to give fhreo-4-hydroxy-3-phenyl-2-heptanone. Ether or ether-dimethoxyethane mixtures are the most suitable... 

U.S. production of w-butanol has increased to 600 kt per annum, largely for conversion to unsaturated esters and saturated ester and ether solvents, while 2-ethylhexanol (about 300 kt per annum in the U.S., but much higher in Europe with exports at 250 kt per annum) is used mainly for the phthalate ester as a plasticizer for PVC. The n- and iso-butyraldehydes are also subjected to aldol condensation/crossed Cannizzaro reactions with formaldehyde, to give the polyols trimethylol-propane (2, 2-bishydroxymethyl-l-butanol) and neopentyl glycol (2,2-dimethyl-1,3-propanediol). 

Today the installed hydroformylation capacity worldwide is more than 7.5 Mio tons per year (Baerns et al., 2006). The most important feedstock is propene, with the products n-butyraldehyde and iso-butyraldehyde (Scheme 6.14.3). The most important single product from propene hydroformylation is 2-ethyl-l-hexanol (>50% of the n-butyraldehyde production), the aldol condensation product obtained from n-butanal, which is an important plasticizer alcohol. After esterification with phthalic anhydride, dioctyl phthalates plasticizers are obtained that are used mainly in poly(vinyl chloride) plastics. 

From 1974 onwards, Rh-based hydroformylation became industrial. The use of a catalyst metal that is about 1000-times more expensive than cobalt was driven by several reasons. First, Rh-hydroformylation is more active and thus requires much lower process pressures (lower energy consumption in compression units) and smaller reactors. Second, Rh-hydroformylation shows a very high selectivity to the aldehyde product with only minimal hydrogenation activity being observed. This is of particular importance for propylene hydroformylation where butyl alcohol is not the principle market use. In contrast, for the desired end-use of w-butyraldehyde in the form of its aldol condensation product 2-ethylhexanol a pure aldehyde feed is required as hemiacetals (formed by reaction of aldehyde and alcohol) complicate product purification and add to operating costs. 

Nolen et al. also reported the self-condensation reaction of butyraldehyde and the cross-aldol condensation of benzaldehyde with acetone (Figs. 9.58 and 9.59) at 250°C. The butyraldehyde self-condensation produced a number of products, including 2-ethyl-2-hexenal, 2-butyl-2-butenal, and 2-ethyUiexanal. The results from the condensation of butyraldehyde indicate that a 40% yield of 2 -ethyl-2 -hexenal is achieved before the formation of by-products becomes dominant. In addition, investigations of the back reaction show that a substantial quantity of butyraldehyde is formed when 2-ethyl-2-hexenal is subjected to water at 250°C. The condensation reaction of benzaldehyde with acetone produced a 15% yield of trans-4-phenyl-3-buten-2-one in 5 h and very small quantities of trans,trans-dibenzylidene acetone during this same period of time. The authors suggest that the low yield could be a result of equilibrium limitations. 

A more difficult mixed aldol condensation to bring about efficiently is one involving two carbonyl compounds, both of which can form enolate ions, especially if one (or both) are aldehydes. One procedure which has been devised to effect such condensations in a controlled manner utilizes metalloenamines as enolate equivalents (see Chapter 1, Section 1.9) and is referred to as a directed aldol condensation The method can be illustrated by considering the mixed aldol condensation of butyraldehyde and acetaldehyde with the objective of preparing 2-hexenal. It is easy to see that the proposed conversion will be accompanied by... 

Many aldols dehydrate spontaneously at room temperature or upon acidification by acetic acid. Thus, the condensation of benzaldehyde with propionaldehyde or butyraldehyde gives the a-alkylcinnamaldehydes directly (58-67%). ... 

Some 2,4-dideoxyhexoses of type 17 (R H, OMe, Q, N3 have been made by condensation of aldehydes RCH2CHO with acetaldehyde, catalysed by 2-deoxyribose-S-phosphate aldolase in these novel en madc aldol reactions, acetaldehyde adds to the substituted aldehyde to give a 3-hydroxy-4-substituted butyraldehyde which that adds another acetaldehyde... 

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