Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Tischenko products

The checkers report that GLC analysis (Note 13) at this point shows that the product is contaminated with ca. 4% of trans-stilbene oxide and <1% of the Tischenko product (Note 14). [Pg.50]

Gas chromatography conditions are as follows Supelco fused silica capillary SPB-1 column (30 m, 0.32-mm ID, 0.25 micrometers df), 100°C initial temperature, 280°C final temperature, 10°C/min. The following retention times were obtained diphenylacetaldehyde (6.7 min), trans-stilbene oxide (7.4 min), Tischenko product (18.2 min). [Pg.50]

The rearrangement is considerably faster when the reaction solution is more concentrated. If 480 mL of dichloromethane is used, the rearrangement is complete within 20 min at -20°C. However, the checkers found that the crude product is contaminated with 3-10% of the Tischenko product (Note 14), which is difficult to remove by chromatography. This by-product can be removed by vacuum distillation (bp 136-144°C, 2 mm). Using this combined purification procedure, the checkers obtained 9.6 g (81%) of diphenylacetaldehyde of >99% purity by capillary GLC analysis (Note 13). [Pg.203]

In the presence of 2-5 mol% of (76) reactions of primary and secondary benzyl alcohols gave Oppenauer products in good to excellent yield, although reactions of primary alcohols having simple alkyl chain gave Oppenauer products in only poor yield since rapid formation of homo- and cross-Tischenko products. Under these conditions, cheap acetone instead of pivalaldehyde can be used as an oxidizer. [Pg.275]

The nameplate capacities for acetaldehyde production for the United States in 1989 are shown in Table 5 (120). Synthetic pyridine derivatives, peracetic acid, acetate esters by the Tischenko route, and pentaerythritol account for 40% of acetaldehyde demand. This sector may show strong growth in some products but all of these materials maybe prepared from alternative processes. [Pg.53]

The Tischenko reaction is a related transformation where the product is an ester. [Pg.471]

Isobutyl isobutyrate, the Tischenko condensation product of two molecules of isobutyraldehyde, is a slow evaporating ester solvent that has been promoted as a replacement for ethoxyethyl acetate. Although produced primarily by the acetylation of isobutyl alcohol, some isobutyl acetate is produced commercially by the crossed Tischenko condensation of isobutyraldehyde and acetaldehyde. Isobutyl acetate [110-19-0] is employed mainly as a solvent, particularly for nitrocellulose coatings. [Pg.380]

Ethyl acetate is an oxygenated solvent widely used in the inks, pharmaceuticals and fragrance sectors. The current global capacity for ethyl acetate is 1.2 million tonnes per annum. BP Chemicals is the world s largest producer of ethyl acetate. Conventional methods for the production of ethyl acetate are either via the liquid phase esterification of acetic acid and ethanol or by the coupling of acetaldehyde also known as the Tischenko reaction. Both of these processes require environmentally unfriendly catalysts (e.g. p-toluenesulphonic acid for the esterification and metal chlorides and strong bases for the Tischenko route). In 1997 BP Chemicals disclosed a new route to produce ethyl acetate directly from the reaction of ethylene with acetic acid using supported heteropoly acids... [Pg.251]

Commercial acrolein (Shell Chemical Corp.) was distilled and shaken with an equal volume of anhydrous calcium sulfate for 30 minutes. The acrolein (containing an impurity of 3.5% of propionaldehyde) was distilled again just before use (b.p., 52.5—52.9° C.). Oxidation products identified using acrolein (99.9% purity) without propionaldehyde, which was removed by the Tischenko reaction (31). Solvents were used after purification (especially dehydration) by conventional methods. [Pg.133]

Cross aldol reaction between two different aldehydes and/or ketones without prior activation or protection should provide a straightforward methodology for the synthesis of aldols, Mahrwald recently reported that treatment of aldehydes with TiCU and NEta (or TMEDA) gives rise to syn- do reaction in good yields (Eqs 38 and 39) [141], This method was extended to the aldehyde-ketone cross aldol reaction catalyzed by TiCU [142], an advantage of which is that reaction occurs at the more encumbered a-position of unsymmetrical ketones, as illustrated in Eqs (40) and (41) [143], The use of aliphatic aldehydes instead of PhCHO usually reduced stereoselectivity. When TiCU was replaced by a catalytic amount of BuTi(0-/-Pr)4Li, the aldol reaction was followed by the Tischenko reaction [144], Methyl vinyl ketone trimerized to give a chlorinated cyclic product with TiCU [145],... [Pg.673]

Reactions of organosamarium(II) halides with aldehydes are sranewhat more complicated and synthetically less useful than those with ketones. The ability of Sm species to serve as strong reducing agents introduces a number of alternative reaction pathways. For example, reaction of EtSmI with benzalde-hyde provides a mixture of benzyl alcohol, benzoin, hydrobenzoin, and benzyl benzoate in low yields. Die first three products presumably arise from benzaldehyde ketyl, generated by single-electron transfer from the Sm reagent to benzaldehyde. The benzyl benzoate apparently is derived frmn a Tischenko-type condensation reaction between a samarium alkoxide species and benzaldehyde. [Pg.254]

Woerpel has recently reported a tandem double asymmetric aldol/C=0 reduction sequence that diastereoselectively affords propionate stereo-triads and -pentads commonly found in polyketide-derived natural products (Scheme 8-2) [14], When the lithium enolate of propiophenone is treated with excess aldehyde, the expected aldolates 30/31 are formed however, following warming to ambient temperature a mono-protected diol 34 can be isolated. In a powerful demonstration of the method, treatment of 3-pentanone with 1.3 equiv of LDA and excess benzaldehyde yielded product in corporating five new stereocenters in 81% as an 86 5 5 3 mixture of diastereomers (Eq. (8.8)). A series of elegant experiments have shown that under the condition that the reaction is conducted, the aldol addition reaction is rapidly reversible with an irreversible intramolecular Tischenko reduction serving as the stereochemically determining step (32 34, Scheme 8-2). [Pg.233]

The Tischenko reaction involves single or double hydride transfer and is readily promoted by the bidentate aluminum reagent (Scheme 6.127) [168] the product in which two aldehydes were assembled was isolated quantitatively. [Pg.265]

New C-0 bonds are formed in the CO/H2 synthesis when CO is converted to CO2 by the WGS reaction (3) and in the synthesis of esters. Only the latter will be discussed here. Primarily methyl esters are formed, and they are significant side products over the (Cs)/Cu/ZnO catalysts but not over the alkali/(Co)/M0S2 catalysts. The mechanism for methyl ester formation has been suggested (ref. 39) to occur via a coupling of a Cn aldehyde with a Ci aldehyde by the Cannizzaro reaction or by a nucleophilic attack of a Cn aldehyde by methoxide (Tischenko reaction). The exception is the formation of methyl formate that occurs via a nucleophilic attack of CO by adsorbed methoxide e... [Pg.120]

Prior to the advent of organocatalysis, the asymmetric direct a-allqtlation reaction was relatively unknown. Classical methods to access a-allq lated carbonyl products required stoichiometric amounts of preformed aldehyde metal enolates. Additionally, side reactions such as aldol, Canizzaro- or Tischenko-type processes diminished the efficiency of these reactions. In this sense the asymmetric intermolecular Sjj2 a-alkylation of aldehydes with simple allq l halides has been a difficult feat to achieve. [Pg.96]

Central in heavy-ends formation is the high reactivity of aldehyde products, in aldol condensation, Tischenko reaction [5], acetalization and oxidation reactions. Aldol condensation is base-catalyzed, acetal formation is acid-catalyzed, so it is important to keep the process medium more or less neutral. Acetals formation can only take place if alcohol by-product is produced (or if a hydroxy group is part of the feedstock/product). [Pg.207]

In lMs connection it is interesting to note that finely divided nickel is iej>orted to accelerate tlie reaction . (An alternative mechanism invoh es the Tischenko reaction with production of method formate, which is readily hydrolyzed in aqueous solution ). [Pg.106]


See other pages where Tischenko products is mentioned: [Pg.50]    [Pg.98]    [Pg.50]    [Pg.98]    [Pg.143]    [Pg.45]    [Pg.132]    [Pg.143]    [Pg.252]    [Pg.436]    [Pg.194]    [Pg.123]    [Pg.101]    [Pg.313]    [Pg.45]    [Pg.1021]    [Pg.284]    [Pg.254]    [Pg.127]    [Pg.323]   
See also in sourсe #XX -- [ Pg.275 ]




SEARCH



© 2024 chempedia.info