Aldehydes ambient concentrations

Measurements were conducted in Rotterdam during the period Januaiy-March 1973, to determine the ambient concentrations of aliphatic aldehydes. The 24-h average concentrations were around 5 ng/m, and the 8 00 a.m.-4 00 p.m. average concentration was 8.4 ng/m (data from L. J. Brasser). 

Aldehydes and ketones are the dominant oxygenates found within the lower troposphere. As discussed in chapters IV, V, and IX, aldehydes and ketones are reactive towards OH radicals and readily undergo photodecomposition in sunlight. Table I-D-1 lists representative measurements of the ambient concentrations of several oxygenates. Data are shown for regions classified as Urban, Rural, and Remote. 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

A mixture of lead(iv) acetate (20 mmol) and KOAc (100 mmol) in AcOH (30 ml) was treated with the neat aldehyde-derived silyl enol ether (20mmol) at ambient temperature. After being stirred for 1 h at ambient temperature, the reaction mixture was diluted with water (30ml), and then extracted with pentane (3 x200ml). The combined pentane extracts were washed with saturated sodium hydrogen carbonate solution (2x50ml), dried, concentrated and distilled to give the product a-acetoxyaldehyde (45-78%). 

Before showing how direct peroxidation of active group works, it should be mentioned that platinum catalyses oxidation of alcohols at ambient temperature in aldehydes (provided they are primary). The exothermicity of the reaction is sufficient to cause the alcohol to combust by heating a thread of platinum at a high temperature. Note that 2-butanol (but not isopropanol) is classified in list B, producing peroxides that become expiosive at a certain concentration in the lists of peroxidable compounds set up by Du Pont de Nemours company (see p.261). 

Heptyl 3-Phenylpropyl Ether [Electrogenerated Acid-Promoted Reduction of an Aldehyde to an Unsymmetrical Ether].333 A mixture of 1-heptanal (1.0 mmol), 3-phenylpropoxytrimethylsilane (1.2 mmol), tetra-n-butylammonium perchlorate (0.1 mmol), and lithium perchlorate (0.1 mmol) was dissolved in CH2CI2 (3 mL) in an undivided cell. The mixture was electrolyzed under constant current (1.67 mA cm-2) with platinum electrodes at ambient temperature. After 5 minutes, dimethylphenylsilane (1.2 mmol) was added drop-wise and the electrolysis was continued (0.06 Faraday/mol). After completion of the reaction, one drop of Et3N was added and the solution was concentrated. The residue was chromatographed on Si02 to give 1-heptyl 3-phenylpropyl... 

No information was found in the available literature on concentrations of endrin aldehyde or endrin ketone in ambient outdoor air or in indoor air. In addition, no information was available on occupational exposures to these chemicals. 

Very little recent information on concentrations of endrin in water could be found in the available literature. Unlike DDT, chlordane, aldrin/dieldrin, and a variety of other chlorinated pesticides, endrin was never used extensively in urban areas. This is reflected in the results from EPA s Nationwide Urban Runoff Program, which showed no detections in 86 high-flow water samples from 51 urbanized watersheds from 19 cities (Cole et al. 1984). Analysis of EPA STORET monitoring information from ambient surface water showed a significant percentage of detections for endrin (32% of 8,789 samples), but most were near the detection limits, with a national median concentration of 0.001 ppb (Staples et al. 1985). A similar analysis of STORET data for endrin aldehyde showed that this compound was not found in 770 samples of ambient surface water. More recently, endrin was not detected (detection limit 49 ng/L [0.045 ppb]) in surface water from the Yakima River Basin, Washington (Foster et al. 1993). However, in... 

TABLE 11.9 Some Typical Concentrations of Aldehydes and Ketones in Ambient Air (ppb)... 

The procedures used to determine ambient carbonyl concentrations involve a collection step with silica or C18 cartridges impregnated with 2,4-dinitrophenylhydrazine. Contamination is inevitable with this system, and blanks must be used to compensate for the degree of contamination. Selection of the appropriate blank values to subtract is a difficult and uncertain process. Consequently, development of a gas chromatographic system that will resolve and respond to the low-molecular-weight aldehydes and ketones is needed. The mercuric oxide and atomic emission detectors should provide adequate response for the carbonyls. 

After setting up a calibration curve (r = 0.996), unknown aminosilane concentrations in toluene solvent could be quantified. The total deposited amount of APTS was calculated from analysis of the residual amount of aminosilane in the solvent. Analysis was performed after two hours of reaction and consecutive filtration under ambient atmosphere. 150 /d aliquots of the salicylic aldehyde and the diethylether were added to 10 ml samples of the filtrate. Absorbance was measured one hour after the ether addition. The calculated loading value yields the total surface loading, including chemical and physical deposition, in the loading step. 

A convenient catalyst precursor is RhH(CO)(PPh3)3. Under ambient conditions this will slowly convert 1-alkenes into the expected aldehydes, while internal alkenes hardly react. At higher temperatures pressures of 10 bar or more are required. Unless a large excess of ligand is present the catalyst will also have some isomerization activity for 1-alkenes. The internal alkenes thus formed, however, will not be hydroformylated. Accordingly, the 2-alkene concentration will increase while the 1-alkene concentration will decrease this will slow down the rate of hydroformylation. This makes the rhodium triphenylphosphine catalyst... 

A reaction vessel was charged with 500 ml diethyl ether, then cooled to 0°C, and NaH (400 mmol) and 23.2 ml ethyl alcohol added followed by 3-pyridine carbox-aldehyde (200 mmol) and 84.8 ml A A-dimethyl glycine ethyl ester. The mixture stirred overnight at ambient temperature and was then heated 1 hour at 30°C. The mixture was transferred to a separation funnel and diluted with 500 ml apiece EtOAc and water. The organic phase was transferred to a beaker, then treated with 500 ml 1M HC1, stirred 10 minutes at ambient temperature, and the phases separated. The aqueous layer was neutralized with solid NaHC03 and extracted three times with 300 ml EtOAc. The combined extracts were dried with Na2S04, concentrated, and an yellow solid isolated. The residue was recrystallized using EtOAc/hexanes, 4 1, and the product isolated in 52% yield as a pale yellow solid. 

Respiratory irritant mixtures can arise from environmental chemical reactions. For example, ozone reacts rapidly with terpenes under environmental ambient conditions to produce aldehydes, ketones, and carboxylic acids. Several studies that have been carried out demonstrated that reaction of ozone with a-pinene, c/-limonene, and isoprene produce low level concentrations (at or below NOEL levels) of oxidation products and that along with residual ozone and terpenes act as respiratory irritants. 1012 Table 17.3 lists the species typically contained in these mixtures along with their K values. As can be seen, the mixtures contain lipophiles (residual terpenes) and hydrophiles (the reaction products). Similar results have also been reported for environmental reaction of terpenes with ozone and nitrogen dioxide. 9 ... 

Under argon, to a solution of (2 )-(+)-BINOL (0.132 g, 0.46 mmol) over 4 A molecular sieves (0.732 g) in methylene chloride (2.8 mL) was added Ti(Ot-Pr)4 (0.069 mL, 0.23 mmol). The resulting deep solution was stirred at ambient temperature for 1.5 h then treated with a solution of the aldehyde (0.5 g, 2.9 mmol) in methylene chloride (1.3 mL). The solution was stirred for 2 min, cooled to 0 °C, treated with tlie allylstannane (1.15 g, 3.2 mmol) over 2 min, and maintained at this temperature for 4.5 h. The reaction was then quenched with saturated sodium bicarbonate, extracted with EtOAc (3x), dried over magnesium sulfate, and concentrated in vacuo. The crude product was purihed via hash chromatography using EtOAc hexanes (1 9) to afford 0.495 g (70%) of the an/z-alcohol and 28 mg (4%) of the 5yn-alcohol as colorless oils. 

To HMDS (22 mmol) was added n-BuLi (20 mmol, 2.5 m in hexane) over 5 min at ambient temperature. After being stirred for 15 min, the solution was cooled to 0°C, and THF (36 ml) was added. After a further 20 min at 0°C, the freshly distilled aldehyde (20 mmol) was added over 7 min. The resulting solution was stirred for 30 min at 0 °C, and then TMSC1 (20 mmol) was added in one portion. After a further 40min, the reaction flask was transferred directly to a rotary evaporator, and the solvent was removed under reduced pressure. The residue was diluted with pentane (15 ml) and filtered rapidly through Celite. Concentration and distillation under reduced pressure (Kugelrohr) gave the pure /V-trimethylsilylaldimine (76-95%). 

The concentrations of aldehydes and phenols in ambient air or in test chambers are generally well below 100 pg/m. The concentrations of diisocyanate monomers are in the magnitude of ng/m. This requires suitable measurement strategies and sensitive techniques for sampling and analysis (see Table 1.2-1). 

This review covers the catalytic literature on condensation reactions to form ketones, by various routes. The focus is on newer developments from the past 15 years, although some older references are included to put the new work in context. Decarboxylative condensations of carboxylic acids and aldehydes, multistep aldol transformations, and condensations based on other functional groups such as boronic acids are considered. The composition of successful catalysts and the important process considerations are discussed. The treatment excludes enantioselective aldehyde and ketone additions requiring stoichiometric amounts of enol silyl ethers (Mukaiyama reaction) or other silyl enolates, and aldol condensations catalyzed by enzymes (aldolases) or catalytic antibodies with aldolase activity. It also excludes condensations catalyzed at ambient conditions or below by aqueous base. Recent reviews on these topics are those of Machajewski and Wong, Shibasaki and Sasai, and Lawrence. " The enzymatic condensations produce mainly polyhydroxyketones. The Mukaiyama and similar reactions require a Lewis acid or Lewis base as catalyst, and the protecting silyl ether or other group must be subsequently removed. However, in some recent work the silane concentrations have been reduced to catalytic amounts (or even zero) this work is discussed. 

Nasr-El-Din et al. (2002) have also investigated the corrosion inhibition of some aldehyde-based sulfide-snppression chemicals on steel conpons in a corrosion autoclave in acidic media. Formaldehyde was mentioned in the research, bnt other aldehyde-based chemicals were only tagged Aldehyde A, Aldehyde and so forth. Combinations of some of these aldehyde-based chemicals were also investigated. They condncted the tests at 0.5 mol% H2S with varying concentrations of sulfide scavengers at ambient, 150°F, and 275°F conditions of temperatures and at pressures of 3000 and 5000 psi. All the corrosion tests were completed at 4 h contact time. They concluded that all the chemicals are effective to some extent in controlling H2S and in corrosion inhibition. 

---