Condensation Of Acetaldehyde Research Articles

In vivo study of salsolinol produced by a high concentration of acetaldehyde in the striatum and nucleus accumbens of free-moving rats.

Salsolinol, a neuropharmacologically active compound, is formed by the condensation of acetaldehyde (AcH) with dopamine (DA) in the brain. The aim of our study was to examine the effect of a high concentration of AcH on salsolinol formation and to compare the release of DA, serotonin (5-HT), and salsolinol in the striatum and nucleus accumbens (NAc) in free-moving rats. After the insertion of a microdialysis probe, male Wistar rats (250-300 g) were treated with cyanamide (CY, a potent aldehyde dehydrogenase inhibitor) + ethanol (EtOH), CY + 4-methylpyrazole (4-MP, a strong alcohol dehydrogenase inhibitor) + EtOH, 4-MP + EtOH, CY, and 4-MP. Simultaneous quantitation of DA, 5-HT, and salsolinol in dialysates was performed by using in vivo microdialysis coupled with high-performance liquid chromatography with an electrochemical detector and blood EtOH and AcH by using a head-space gas chromatographic method. Salsolinol was detected only in the CY + EtOH groups in both the striatum and NAc, and we also detected a high AcH concentration in the blood in those groups. A correlation was found between the dialysate levels of salsolinol and blood concentrations of AcH. The striatal levels of DA and 5-HT were approximately two times higher, whereas salsolinol levels were approximately three times higher compared with the usual level in the NAc. No significant difference of DA and 5-HT levels in the dialysates was observed in either the control or the other study groups. Our observation suggested that the brain salsolinol formation may depend on the concentrations of DA and AcH in freely moving rats, and there is no effect of a high concentration of AcH on DA and 5-HT levels in the striatum and NAc.

The aldol condensation of acetaldehyde and heptanal on hydrotalcite-type catalysts

The aldol condensation of acetaldehyde and heptanal has been carried out in the liquid phase between 353 and 413 K using different types of solid base catalysts: MgO with strong Lewis basic sites, Mg(Al)O mixed oxides with acid–base pairs of the Lewis type obtained from hydrotalcite precursor, and rehydrated Mg(Al)O mixed oxides with Brønsted basic sites. The influence of several reaction parameters, temperature, acetaldehyde to heptanal molar ratio, nature of solvent (hexane, toluene, ethanol), has been investigated. A comparative study of the catalysts has been performed in the such defined optimal reaction conditions, i.e., 373 K, acetaldehyde/heptanal molar ratio, 2/1; and ethanol/reactants molar ratio, 5/1. Mg(Al)O mixed oxides calcined below 673 K are the most selective catalyst to 2-nonenal, the cross-condensation product formed when in the first step proton abstraction occurs from acetaldehyde. Acid–base pairs of moderate basic strength are suitable when this cross-condensation is the desired reaction. Stronger Lewis basic sites of MgO or Brønsted-type basic sites of the rehydrated mixed oxide tend to favor the formation of carbanion from heptanal. This latter leads to the formation of 2-pentyl-2-butenal and 2-pentyl-2-nonenal by cross-condensation with acetaldehyde and self-condensation, respectively.

The Prebiotic Synthesis of Acrolein

Acrolein is a central intermediate in the prebiotic synthesis of several amino acids, pentaerythritol, as well as various postulated alternative genetic materials. Acrolein is highly reactive so that its steady-state concentration could not have been very high. The ease of synthesis of acrolein from the aqueous aldol condensation of acetaldehyde and formaldehyde was therefore of interest. It is shown here that acrolein is produced in a low, but significant, steady-state concentration from very dilute solutions of formaldehyde and acetaldehyde under neutral to basic conditions. Acrolein is produced under conditions that are too dilute for the oligomerization of formaldehyde to produce carbohydrates. The implications of these findings for prebiotic chemical evolution are discussed.

Effect of oxygenation on polyphenol changes occurring in the course of wine-making

The influence of controlled oxygenation on the colour and phenolic composition of red wine was studied by UV–VIS spectrophotometry, liquid chromatography (LC) coupled to diode array detection (DAD) and electrospray ionisation mass spectrometry, and thiolysis. The comparison between the control and oxygenated wines demonstrated changes in colour characteristics along with a significant increase in concentrations of pyranoanthocyanins, ethyl-bridged compounds and derived pigments both with storage time and with oxidation. Principal component analysis was applied to wine analysis data measured throughout the conservation period. The effect of the storage time and oxygenation was clearly reflected in this analysis. Mass-spectrometric analysis of the wines demonstrated the presence of compounds which are markers of reactions involving acetaldehyde. Two types of mechanisms were observed. The first concerns acetaldehyde condensation reactions and the second, the cycloaddition process between anthocyanins and flavanols mediated by acetaldehyde, generating tannin-pyranoanthocyanins. The presence in wines of trimeric structures resulting from these mechanisms, as well as the results obtained after thiolysis of the fraction containing polymeric species obtained by Fractogel chromatography, confirm that proanthocyanidins react with acetaldehyde in the same way as flavanol monomers.

Elucidation of the mechanism of pyrrole formation during thermal degradation of 13C-labeled l-serines

Pyrolysis of [13C-1], [13C-2] and [13C-3]-labelled l-serines generated mono-substituted methyl and ethyl derivatives of pyrroles and pyrazines among other compounds. Analyses of label incorporation into the pyrroles have indicated their formation through aldol condensation of acetaldehyde with different α-aminocarbonyl compounds followed by cyclization and loss of water (Knorr pyrrole synthesis). Comparison of the label incorporation patterns of the α-aminocarbonyls involved in the formation of methyl and ethyl-substituted pyrroles with that of similarly substituted pyrazines, revealed their common origin. In addition, α-aminocarbonyls involved in the formation of 2- and 3-substituted pyrroles had identical label distribution patterns, indicating their formation through the same carbonyl precursors. Furthermore, the major pathway (55%) leading to the formation of the α-aminocarbonyl precursors of methyl-substituted pyrroles involved aldol addition of formaldehyde to glycolaldehyde, whereas the only pathway leading to the formation of the α-aminocarbonyl precursors of ethyl-substituted pyrroles involved the interaction of alanine — formed in situ — with glycolaldehyde.

Gas and vapor sorption and diffusion in poly(ethylene terephthalate)

Equilibrium sorption of n-butane and acetaldehyde in melt-processed poly(ethylene terephthalate) (PET) microtomed flakes is reported. The n-butane sorption isotherm at 35°C is well described by the dual-mode model with the following parameters: kD=0.017cm3 (STP)/(cm3 amorphous polymer cmHg), C′H=1.3cm3 (STP) (cm3 amorphous polymer) and b=0.029cmHg−1. Acetaldehyde isotherms at 35 and 45°C may be described by the Flory–Huggins sorption model, suggesting that penetrant uptake in the non-equilibrium excess volume associated with the glassy polymer made a negligible contribution to the overall sorption level at the conditions of this study. The heat of sorption was essentially equal to the enthalpy of condensation of pure acetaldehyde. At 45°C and acetaldehyde pressures at or above 40.0cmHg, acetaldehyde triggers significant crystallization of PET (up to 37wt%) with increasing concentration. Subsequent sorption experiments at very low penetrant activity reveal solubility coefficients that are markedly higher in the penetrant-crystallized sample than in the initially highly amorphous sample. This result suggests the acetaldehyde-induced formation of microvoids (which act as highly efficient penetrant sorption sites) in the polymer sample. Based on these and literature data, the logarithm of infinite dilution penetrant solubility in amorphous regions of PET was well-correlated with penetrant condensability as characterized by Tc, penetrant critical temperature, or by (Tc/T)2, where T is the experiment temperature. Infinite dilution, amorphous phase penetrant diffusion coefficients in PET decreased according to a power law relation with increasing penetrant critical volume.

The aldol condensation of lower aldehydes over MFI zeolites with different acidic properties

Various MFI type zeolites were synthesized taking into account two factors affecting zeolitic acidity “by synthesis”, namely the nature of the substituted heteroelement and the Si/Me 3+ ratio. The surface properties with respect to chemical composition and acidity were investigated by temperature-programmed reduction, X-ray photoelectron spectroscopy, temperature-programmed desorption of ammonia, Fourier transform infrared spectroscopy and microcalorimetry. Vapor phase aldol condensation of acetaldehyde and formaldehyde over these catalysts has been carried out, and it has been observed that the structural features of the catalysts do play an important role in controlling conversion and selectivity. A reasonable acidity and activity relationship is established. A mechanism for cross-aldol condensation involving both Brönsted and Lewis acid sites is proposed.

Oxidation of ethane into acetaldehyde and acrolein over silica containing cesium and a very small amount of additives

Many samples containing different elements M in the system of M/SiO 2 (M : Si = 1 : 1000, molar ratio) or Cs/M/SiO 2 (Cs : M : Si = 10 : 1 : 1000, molar ratio) were prepared and screened for the oxidation of ethane by use of oxygen as oxidant. It has been found that the elements M (M = V, Bi, In, Ga, P, Zr, Zn, La) can give good aldehyde yields in the Cs/M/SiO 2 system. The promoting effects of different alkali metals (Li, Na, K, Rb, Cs) on the catalytic performance of V/SiO 2 (V : Si = 1 : 1000) in ethane oxidation were investigated. Among them, cesium gave the best promoting effect on V/SiO 2 for aldehyde formation. The presence of alkali metals increases the basicity and neutralizes the acid site of catalyst; thus it enhances the selectivity to acetaldehyde and controls the formation of formaldehyde. Increase in basicity promotes the cross-aldol condensation of acetaldehyde and formaldehyde to give acrolein. The pathway for acrolein formation is mainly through the cross-aldol condensation of acetaldehyde and formaldehyde over Cs/V/SiO 2 catalysts.

Formation of sugar-specific reactive intermediates from (13)C-labeled L-serines.

Analysis of the pyrolysis products of [1-(13)C], [2-(13)C], and [3-(13)C]-labeled L-serines has indicated the presence of three initial degradation pathways. Decarboxylation followed by deamination produces aminoethanol and acetaldehyde, respectively; a retro-aldol pathway generates formaldehyde and glycine. Dehydration of L-serine can lead to the formation of pyruvic acid, which eventually can be converted into the amino acid alanine. Formation of alanine and glycine was confirmed due to the detection of 2, 5-diketo-3,6-dimethylpiperazine and cycloglycylalanine. Most of the advanced decomposition products of L-serine can be rationalized on the basis of these initial degradation products. Label incorporation studies have elucidated the origin of carbonyl precursors of methyl- and 2,3-dimethylpyrazines formed in the thermal decomposition mixture of L-serine. Three mechanistic pathways were identified for the formation of carbonyl precursors of methyl- and 2, 3-dimethylpyrazines. The major pathway (70%) for the formation of the precursor of methylpyrazine involved aldol addition of formaldehyde to glycolaldehyde to form glyceraldehyde. On the other hand, the major pathway (60%) for the formation of the precursor of 2,3-dimethylpyrazine involved an aldol condensation of acetaldehyde with glycolaldehyde to form 2,3-butanedione.

Synthesis of 3-cyano-3-ethoxycarbonyl-4-methyl-6-phenylpyridine-2(1H)-thione and its alkylation

The condensation of acetaldehyde with cyanothioacetamide and ethyl benzoylacetate in the presence of N-methylmorpholine leads to the formation of 3-cyano-5-ethoxycarbonyl-4-methyl-6-phenylpyridine-2(1H)-thione. Alkylation of the last afforded the corresponding substituted 2-alkythiopyridines.

Influence of the acid–base properties of solid catalysts derived from hydrotalcite-like compounds on the condensation of formaldehyde and acetaldehyde

The vapor-phase aldol condensation of formaldehyde with acetaldehyde was studied using various oxide mixtures obtained in situ from hydrotalcite-like materials as catalysts. All samples exhibited catalytic activity, but the selectivity to both the aldol condensation and the acrolein formation is governed by the balance of acidic and basic properties. The oxides containing Mg and Al or Co and Al showed a high selectivity to aldol condensation (90% at 300°C) as well as to cross-condensation (80% at 300°C). The effects of both the reaction variables (temperature, mole ratio of reagents) and the catalyst variables (nature of cations, nature of anions) were studied.

Competition between Acetaldehyde and Crotonaldehyde during Adsorption and Reaction on Anatase and Rutile Titanium Dioxide

The adsorption of acetaldehyde and crotonaldehyde on the anatase and rutile polymorphs of TiO2 has been investigated with Fourier transform infrared spectroscopy (FTIR). Chemisorption of acetaldehyde on TiO2 involves a strong interaction between the surface and the carbonyl oxygen, causing a significant shift in the location of the ν(CO) vibrational mode to lower frequencies; no interaction with surface hydroxyl groups was observed. Capacities for acetaldehyde and crotonaldehyde adsorption under conditions relevant to aldolization reactions were determined in a novel reactor system providing simultaneous mass measurements and mass spectral analysis of gas-phase products. The coverage of acetaldehyde irreversibly adsorbed on TiO2 was similar to values previously reported for the adsorption of alcohols; coverages of crotonaldehyde were approximately 60% of those for acetaldehyde. Both gas-phase and surface analyses indicate that formation of crotonaldehyde by aldol condensation of acetaldehyde occurs on rut...

Aldol condensation of acetaldehyde to form high molecular weight compounds on TiO 2

Temperature-programmed desorption, hydrogenation, and oxidation are used to show that acetaldehyde undergoes continued aldol condensation beyond crotonaldehyde formation on Degussa P-25 titania to form hexan-2,4-diene-al and higher molecular weight compounds containing conjugated C=C bonds. Aromatic compounds also form, and at higher temperatures coke forms. Degussa P-25 TiO2 has more sites that catalyze chain propagation reactions beyond formation of C4 species than do pure anatase or rutile surfaces. These reactions may be responsible for deactivation observed during photocatalytic oxidation of acetaldehyde at elevated temperatures.

New methods for the synthesis of alkyl-substituted 6-oxo-3-cyano-1,4,5,6-tetrahydropyridine-2-thiolates and their derivatives

Condensation of formaldehyde or acetaldehyde with cyanothioacetamide and cyanoacetic ester in the presence of organic bases afforded 6-oxo-3,5-dicyano-4-R-1,4,5,6-tetrahydropyridine-2-thiolates (R=H, CH3), which were utilized in the synthesis of substituted 2-alkylthiopyridones and thieno[2,3-b]pyridone.

Structure and Surface and Catalytic Properties of Mg-Al Basic Oxides

Mg-Al mixed oxides with Mg/Al molar ratios of 0.5–9.0 were obtained by thermal decomposition of precipitated hydrotalcite precursors. The effect of composition on structure and surface and catalytic properties was studied by combining several characterization methods with ethanol conversion reactions. The nature, density, and strength of surface basic sites depended on the Al content. On pure MgO, strong basic sites consisted predominantly of O2−anions. Calcined hydrotalcites contained surface sites of low (OH−groups), medium (Mg-O pairs), and strong (O2−anions) basicity. The relative abundance of low and medium strength basic sites increased with the Al content. The addition of small amounts of Al to MgO diminished drastically the density of surface basic sites because of a significant Al surface enrichment. Formation of surface amorphous AlOystructures in samples with low Al content (Mg/Al > 5) partially covered the Mg-O pairs and decreased the concentration of surface O2−anions. At higher Al contents (5 > Mg/Al > 1), the basic site density increased because the Al3+cations within the MgO lattice created a defect in order to compensate the positive charge generated, and the adjacent oxygen anions became coordinatively unsaturated. In samples with Mg/Al < 1, segregation of bulk MgAl2O4spinels occurred and caused the basic site density to diminish. The catalyst activity and selectivity of Mg-Al mixed oxides in ethanol conversion reactions depended on composition. The dehydrogenation of ethanol to acetaldehyde and the aldol condensation ton-butanol both involved the initial surface ethoxide formation on a Lewis acid–strong base pair. Pure MgO exhibited poor activity because the predominant presence of isolated O2−basic centers hindered formation of the ethoxide intermediate by ethanol dissociative adsorption. The incorporation of small amounts of Al3+cations to MgO drastically increased the acetaldehyde formation rate because of the generation of new surface Lewis acid–strong base pair sites. Acetaldehyde condensation towardn-butanol is a bimolecular reaction between adjacent adsorbed acetaldehyde species that requires not only acid–strong base pair sites but also a high density of basic sites; these pathways were favored on Mg-Al samples with higher Al content (5 > Mg/Al > 1). The dehydration of ethanol to ethylene, and the coupling and dehydration to diethyl ether increased with Al content, probably reflecting the density increase of both Al3+-O2−pairs and low- and medium-strength basic sites. Pure Al2O3displayed the highest dehydration activity.

Formation of a fluorescent adduct in the reaction of 2'-deoxyadenosine with a malonaldehyde-acetaldehyde condensation product.

Malonaldehyde (malondialdehyde, MDA) was reacted with 2'-deoxyadenosine in buffered aqueous solution. HPLC analyses of the reaction mixtures showed that, besides the two previously characterized N6-propenal (M1dA) and N6-oxazocinyl (M3dA) adenine adducts, a third compound eluting at longer retention time was formed. The compound generated a strong peak in the chromatogram recorded by a fluorescence detector. The new compound was isolated by preparative C18 chromatography, and its structure was characterized by UV absorbance, fluorescence emission, 1H and 13C NMR spectroscopy, and mass spectrometry. The product was identified as 9-(2'-deoxyribosyl)-6-(3,5-diformyl-4-methyl-1, 4-dihydro-1-pyridyl)purine (M2AA-dA). The yield of the product was 0.8% following 7 days of reaction at 37 degreesC and pH 4.6. Lower yields were obtained at higher pH conditions. By the addition of acetaldehyde, the yield increased about 10-fold at all studied pH conditions. The adduct was most likely formed by an initial condensation of two molecules of malonaldehyde with one molecule of acetaldehyde followed by reaction of the condensation product with the exocyclic amino group of 2'-deoxyadenosine. The identification of this adduct shows that acetaldehyde may react with DNA bases also through an initially formed malonaldehyde-acetaldehyde condensation product.

Condensation of pyrrole with aldehydes in the presence of Y zeolites and mesoporous MCM-41 aluminosilicate: on the encapsulation of porphyrin precursors

Condensation of pyrrole and benzaldehyde was carried out in isooctane or cyclohexane in the presence of MCM-41, HY (Si/Al 15) and CoY (Si/Al 2.6). In all cases, formation of tetraphenylporphyrin (TPP) was observed in the organic solutions, even after dissolving with hydrofluoric acid the resulting MCM-41 solid employed in the condensation. In addition, some reaction intermediates containing one to two pyrrole heterocycles were also characterized in these solutions. In spite of this, the diffuse reflectance and IR spectra of the organic material adsorbed in the aluminosilicates after the condensation reaction were remarkably different from those characteristic of TPP. This discrepancy indicates that the material adsorbed inside the solid pores is not TPP but most probably any of its immediate porphyrinogen precursors. In this regard, the coincidence of the diffuse reflectance spectra obtained after the synthesis with those characteristic of porphomethenes and porphodimethenes was noted. Condensation of pyrrole and acetaldehyde follows the same pattern: lack of formation of meso-tetramethylporphyrin (TMP) inside the pores according to diffuse reflectance and IR spectroscopies, but detectable amounts of TMP in the organic solutions.

Synthesis and alkylation ofN-methylmorpholinium 6-amino-3,5-dicyano-4-methylpyridine-2-thiolate

The condensation of acetaldehyde with a twofold excess of cyanothioacetamide andN-methylmorpholine givesN-methylmorpholinium 6-amino-3,5-dicyano-4-methylpyridine-2-thiolate. This compound is also formed by recyclization of 2,6-diamino-3,5-dicyano-4-methyl-4H-thiopyran. From this pyridinethiolate, several substituted 2-alkylthiopyridines and 3,6-diamino-5-cyano-4-methyl-2-methoxycarbonylthieno[2,3-b]pyridine were obtained.

Vapor phase aldol condensation of acetaldehyde on metal oxide catalysts

Vapor phase aldol condensation of acetaldehyde on silica supported alkali metal containing solid bases, silica supported tungsten and molybdenum oxides and other unsupported oxides were studied. It was found that silica supported alkali metal containing solid base catalysts can effectively catalyze the aldol condensation of acetaldehyde to produce crotonaldehyde as well as crotyl alcohol with a good selectivity (ca. 90%) and stability and moderate conversion. MoO 3/SiO 2 or MoO x/SiO 2 (reduced state) was found to be almost inactive for this reaction. Contrary to MoO 3(MoO x)/SiO 2, WO 3(WO x)/SiO 2 catalysts are active and more selective. Most of other unsupported oxides tested in this study are not attractive for the low activity and selectivity or poor stability. ZrO 2 or pre-treated ZrO 2 SO 4 2− was initially quite active, but deactivated quickly. Co-feeding hydrogen can enhance the activity of ZrO 2 or inhibit deactivation of pre-treated ZrO 2 SO 4 2−. The super acidic site associated with SO 4 2− species has a great contribution to coking but little to aldol condensation.

(+)-Catechin—acetaldehyde condensation products in relation to wine-ageing

Dimers resulting from acetaldehyde-flavanol condensation were studied in an acidic hydroalcoholic medium (12% ethanol pH 3.2) in order to simulate the conditions of wine tannin-transformation during the wine-ageing process. One of the dimers was isolated after hemisynthesis and studied by mass spectrometry, NMR and molecular mechanics. Mass spectrometric analysis was in accordance with a dimeric structure with a CH-CH 3 linkage. NMR showed the presence of a 6–8 (ethane-1,1-diyl)di(+)-catechin. The carbon atoms, C-6 and C-8, involved in the linkage, have, an asymmetric conformation, with the two catechols in an equatorial position.