Aldehydes in aqueous solution

The palladium chloride process for oxidizing olefins to aldehydes in aqueous solution (Wacker process) apparendy involves an intermediate anionic complex such as dichloro(ethylene)hydroxopalladate(II) or else a neutral aqua complex PdCl2 (CH2=CH2)(H2 0). The coordinated PdCl2 is reduced to Pd during the olefin oxidation and is reoxidized by the cupric—cuprous chloride couple, which in turn is reoxidized by oxygen, and the net reaction for any olefin (RCH=CH2) is then... 

An efficient route for the synthesis of the Phe-Phe hydroxyethy-lene dipeptide isostere precursors utilized for the design of potential inhibitors of renin and HIV-protease was developed. The key step is the zinc-mediated stereoselective allylation of A-protected a-amino aldehydes in aqueous solution (Eq. 8.32).70 NaBF4/M (M = Zn or Sn) showed facilitating allylation of a variety of carbonyl compounds in water, and a-and y-addition products of crotylations could be alternatively obtained under the control of this novel mediator (Eq. 8.33).71... 

Dioxatetraazaperhydroanthracenes 98 were prepared by one-pot cyclization reaction of hydrazinoethanols 97 with aldehydes in aqueous solution (Equation 6) <1996JOC4125>. 

Amidoximes readily condense with aliphatic aldehydes in aqueous solution to form 4,5-dihydro-l,2,4-oxadiazoles (oxadiazolines). 

Sham, Y. Y., and J. A. Joens, Temperature Dependent Near-UV Molar Absorptivities of Several Small Aldehydes in Aqueous Solution, Spectrochim. Acta, 51 A, 247-251 (1995). 

It is well known, however, that substituents favor cyclic as against acyclic forms,76 and electron-attracting substituents on the a-carbon atom increase the tendency of carbonyl groups to react with hydroxyl groups (for example, the ratio of aldehydrol to aldehyde in aqueous solution is —1.2 1 for acetaldehyde77 at 25°, and 17.5 1 for glycolalde-hyde78 at 35°). Hence, whereas 6-hydroxy-2-hexanone is found only in the acyclic form, aqueous solutions of the 1-deoxyhexuloses contain only 5% of this form at equilibrium, and those of the hexuloses contain less than 1% (see Table IV). 

In a study of imine formation from aldehydes in aqueous solution, formation constants have been correlated with three parameters the pK.d and HOMO energy of the amine and the LUMO energy of the aldehyde.23... 

Habermann, on electrolyzing the alcohol in alkaline solution, obtained, besides carbon dioxide, an aldehyde resin (Ludersdorf and Connel 6) from which he isolated a body closely related to cinnamic aldehyde. In aqueous solution, on the addition of potassium acetate, the alcohol was split up into ethane, potassium ethyl-carbonate, carbon dioxide, and acetic ester. 

Now what about this slightly more complicated example Sodium cyanide is added to a simple aldehyde in aqueous solution. The product is a cyanohydrin and we shall discuss this chemistry in Chapter 6. 

Table 2 Comparison of the catalytic activity for alcohol oxidation to the corresponding aldehyde in aqueous solution...

Yb(OTf)3 is an excellent catalyst for the aldol reactions of silylenol ethers with aldehydes in aqueous solution, working better than in organic solvents like THF and MeCN, though the reactions can also be performed in organic solvents, and, after the reaction has been quenched by the addition of water, the triflate catalyst may be recovered from the aqueous layer. 

The electroactive species A is generated by a reaction, generally an equilibrium displaced toward Z, that precedes the electron transfer step. Z is the reactant introduced in the cell or the predominant form of the reactant in the reaction medium. These reaction schemes were introduced to rationalize the various electrochemical phenomena observed during the reduction of certain aldehydes in aqueous solutions. Indeed, in water, formaldehyde, r-electron-poor heterocyclic aldehydes, and a few aldehydes with strongly electron-attracting groups exist as their nonreducible hydrated form in rapid equilibrium with the reducible carbonyl ... 

A selective hydrogenation of a, fi-unsaturated aldehydes in aqueous solution was carried out using PTFE capillary of diameter from 500 to 1000 pm [30]. The gas-liquid-liquid flow observed in the reactor is depicted in Figure 8.11. It shows... 

Hirschberg Y, Fargas L (1937) On the photochemical decomposition of aldehydes in aqueous solution. J Am Chem Soc 59 2453-2457... 

The reaction of ascorbic acid with aldehydes in aqueous solutions yields the corresponding hemiacetals. The reaction with methyl-glyoxal (a typical product of carbohydrate degradation) gives rise to two cyclic hemiacetals (5-125). Similar products are produced with acrolein, the degradation product of glycerol. 

Table 7.4 reports a comparison between PCM and classical local (reaction + cavity) field factors for IR intensities of a series of simple aldehydes in aqueous solution [158]. Here/ + /i is obtained as the ratio between the calculated PCM IR intensity (with the account of both reaction and cavity field) and the corresponding value for the isolated molecule. PCM factors are generally different from classical formulations, and the difference is not limited to the same compound, but there is also a discrepancy in the observed trend in passing from one species to another. The largest difference between PCM and classical data is shown by the MSP equation, as reasonably expected due to the fact that MSP does not take into account any dependence on the static dielectric constant of the solvent. Such a dependence is instead present in the reaction field term of the PCM calculated data. 

Table 7.5 IR Intensities Classical fons) and PCM fp) Cavity Field Factors for Selection of Aldehydes in Aqueous Solution...

Hydration of the aldehydes occurs readily, though pyridine-4-aldehyde is the only one which readily gives a crystalline hydrate . The complex equilibria set up by a number of pyridine aldehydes in aqueous solution have been evaluated by means of ultra-violet spectroscopy Forpyridine-2-aldehyde the equilibria have been represented as... 

Mukaiyama aldol reactions, whereby trimethylsilyl enol ethers react with aldehydes in aqueous solution to form -ketoalcohols, have been promoted by new chiral lanthanide-containing complexes and a chiral Fe(II)-bipyridine complex with 0 outstanding diastereo- and enantio-selectivities. Factors controlling the diastereoselec-tivity of Lewis-acid-catalysed Mukaiyama reactions have been studied using DFT to reveal the transition-state influences of substituents on the enol carbon, the a-carbon of the silyl ether, and the aldehyde. The relative steric effects of the Lewis acid and 0 trimethyl silyl groups and the influence of E/Z isomerism on the aldol transition state were explored. Catalytic asymmetric Mukaiyama aldol reaction of difluoroenoxysilanes with /-unsaturated a-ketoesters has been reported for the first time and studied extensively. ... 

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