Aldehydes, detection

Colorimetry. Laboratory data on the persistence of biocides formulated in glutaraldehyde and acrolein are available [1260]. A colorimetric general aldehyde detection method based on m-phenylenediamine was used. Such studies follow the demand for better understanding of ecologic systems in the aspect of environmental protection. 

Hydrates, enthalpies of formation, 156, 157 Hydrazones, aldehyde detection, 670 Hydrocarbons autoxidation, 320... 

Saturated aldehyde (XXII) and a,3 - unsaturated aldehyde (XXI) groups are produced upon decomposition of the monocyclic-peroxide structures and are depicted In the Ir spectra by bands at 1725 and 1700 cm, respectively. Structures (XVa), (XVc), and (XVIa) lead to the saturated and unsaturated pairs, while (XVb) and (XVIb) would yield only saturated aldehydes. In the temperature range of 60-120 0, unsaturated and saturated aldehydes detected are of comparable Intensity, consistent with formation of (XVa), (XVc), and (XVIa). The formation of (XVb) and (XVIb)... 

The evolution of the reaction shows that 23 is isomerized into 22 before the hydroformylation reaction starts, because the M-P-alkyl intermediate is b-ehminated faster than CO is inserted. However, if the reaction is started from 23 and the ligands have small cone angles, such as P(OMe)3, practically the only aldehyde detected is the 3-formyl derivative (entry 3). If it is started from 22, the 3-formyl derivative is the main aldehyde detected (entry 1). This suggests that under these conditions there is no P-elimination process or that it is very slow. 

Calestani D, Mosca R et al (2011) Aldehyde detection by ZnO tetrapod-based gas sensors. J Mater Chem 21(39) 15532-15536... 

Reagent A is particularly useful for the treatment of the lower aliphatic aldehydes and ketones which are soluble in water cf. acetaldehyde, p. 342 acetone, p. 346). The Recent is a very dilute solution of the dinitrophenylhydrazine, and therefore is used more to detect the presence of a carbonyl group in a compound than to isolate sufficient of the hydrazone for effective recrystallisation and melting-point determination. 

The condensation products are almost insoluble in water, but can be crystallised from dilute alcohol. Dimedone is therefore a good reagent for the detection and characterisation of aldehydes. 

The reagent is attacked by oxidising agents with the formation of formaldehyde, hence it cannot be used for the detection of the latter (or of other aldehydes) in the presence of oxidising agents. 

The dimedone reagent may, however, be used if it is desired to detect an aldehyde in the presence of a ketone. 

The polyhydric alcohols of Solubility Group II are liquids of relatively high boiling point and may be detected inter alia by the reactions already described for Alcohols (see 6). Compounds containing two hydroxyl groups attached to adjacent carbon atoms (1 2-glyeols), a-hydroxy aldehydes and ketones, and 1 2-diketones may be identified by the periodic acid test, given in reaction 9. 

METHOD 2 [89]--1M MDA or benzedrine and 1M benzaldehyde is dissolved in 95% ethanol (Everclear), stirred, the solvent removed by distillation then the oil vacuum distilled to give 95% yellow oil which is a Schiff base intermediate. 1M of this intermediate, plus 1M iodomethane, is sealed in a pipe bomb that s dumped in boiling water for 5 hours giving an orangy-red heavy oil. The oil is taken up in methanol, 1/8 its volume of dH20 is added and the solution refluxed for 30 minutes. Next, an equal volume of water is added and the whole solution boiled openly until no more odor of benzaldehyde is detected (smells like almond extract). The solution is acidified with acetic acid, washed with ether (discard ether), the MDMA or meth freebase liberated with NaOH and extracted with ether to afford a yield of 90% for meth and 65% for MDMA. That s not a bad conversion but what s with having to use benzaldehyde (a List chemical) Strike wonders if another aldehyde can substitute. 

When PET is extracted with water no detectable quantities of ethylene glycol or terephthaUc acid can be found, even at elevated extraction temperatures (110). Extractable materials are generally short-chained polyesters and aldehydes (110). Aldehydes occur naturally iu foods such as fmits and are produced metabohcaHy iu the body. Animal feeding studies with extractable materials show no adverse health effects. 

Bacterial concentrations have also been determined by using the enzyme-catalyzed chemiluminescent reaction of reduced flavin mononucleotide (FMN) with oxygen and aldehydes. The detection limit was reported to be 10 ceUs of E. coli, which contains 7 x 10 g of FMN per ceU (303). 

The amino group is readily dia2oti2ed in aqueous solution, and this reaction forms a basis for the assay of sulfas. Aldehydes also react to form anils, and the yellow product formed with 4-(dimethylamino)hen2a1dehyde can be used for detection in thiu-layer and paper chromatography. Chromatographic retention values have been deterrnined in a number of thiu layer systems, and have been used as an expression of the lipophilic character of sulfonamides (23). These values have corresponded well with Hansch lipophilic parameters determined in an isobutyl alcohol—water system. 

The use of an acidic solution of p-anisaldehyde in ethanol to detect aldehyde functionalities on polystyrene polymer supports has been reported (beads are treated with a freshly made solution of p-anisaldehyde (2.55 mL), ethanol (88 mL), sulfuric acid (9 mL), acetic acid (1 mL) and heated at 110°C for 4 min). The colour of the beads depends on the percentage of CHO content such that at 0% of CHO groups, the beads are colourless, -50% CHO content, the beads appear red and at 98% CHO the beads appear burgundy [Vdzquez and Albericio Tetrahedron Lett 42 6691 200]]. A different approach utilises 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald) as the visualizing agent for CHO groups. Resins containing aldehyde functionalities turn dark brown to purple after a 5 min reaction followed by a 10 minute air oxidation [Coumoyer et al. J Comb Chem 4 120 2002]. 

Ethanol [64-17-5] M 46.1, b 78.3 , d 0.79360, d 0.78506, n 1.36139, pK 15.93. Usual impurities of fermentation alcohol are fusel oils (mainly higher alcohols, especially pentanols), aldehydes, esters, ketones and water. With synthetic alcohol, likely impurities are water, aldehydes, aliphatic esters, acetone and diethyl ether. Traces of benzene are present in ethanol that has been dehydrated by azeotropic distillation with benzene. Anhydrous ethanol is very hygroscopic. Water (down to 0.05%) can be detected by formation of a voluminous ppte when aluminium ethoxide in benzene is added to a test portion. Rectified... 

Althoi h the equilibrium constant for hydration is unfavorable, the equilibrium between an aldehyde or ketone and its hydrate is established rapidly and can be detected by isotopic exchange, using water labeled with 0, for example ... 

The R band characteristic for aromatic aldehyde groups (aldehyde n TT bands) occurs in the spectrum of A -methylcotarnine (9a) and that of JV-benzoylcotarnine (9c), which are real aldehydes, at 330 m/i in the form of an inflection. Even in alkaline solution the hypothetical amino-aldehyde form of cotarnine can only occur in amounts not detectable by spectroscopic methods. 

Kinetic investigation of the reaction of cotarnine and a few aromatic aldehydes (iV-methylcotarnine, m-nitrobenzaldehyde) with hydrogen eyanide in anhydrous tetrahydrofuran showed such differences in the kinetic and thermodynamic parameters for cotarnine compared to those for the aldehydes, and also in the effect of catalysts, so that the possibility that cotarnine was reacting in the hypothetical amino-aldehyde form could be completely eliminated. Even if the amino-aldehyde form is present in concentrations under the limit of spectroscopic detection, then it still certainly plays no pfi,rt in the chemical reactions. This is also expected by Kabachnik s conclusions for the reactions of tautomeric systems where the equilibrium is very predominantly on one side. 

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