Ketones ambient concentrations

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. 

Linking the ketone and carboxylic acid components together in an Ugi reaction facilitates the synthesis of pyrrolidinones amenable to library design. The three-component condensation of levulinic acid 30, an amine and isocyanide proceeds under microwave irradiation to give lactams 31 [65]. The optimum conditions were established by a design of experiments approach, varying the equivalents of amine, concentration, imine pre-formation time, microwave reaction time and reaction temperature, yielding lactams 31 at 100 °C in poor to excellent yield, after only 30 min compared to 48 h under ambient conditions (Scheme 11). 

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. 

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. 

To a solution of the catalyst (0.1 mmol), p-toluene sulfonic acid monohydrate (0.1 mmol) and the nitroalkene (0.5 mmol) in DMF (1 mL) was added the ketone (0.25 mmol). The solution was stirred at ambient temperature under reduced pressure, and the residue purified by FC on silica gel. Alternatively, ethyl acetate was added, and the solution washed with water, 1 M HCl, dried (Na2S04), and concentrated to give the crude product which was purified by FC on silica gel. 

NaH, 60% dispersion in oil (18.25 mmol) was suspended in 50 ml THE and triethylphosphonoacetate (19.30 mmol) added. It was stirred 15 minutes at 0°C and trans-3,4 dimethyl-cyclopentyl ketone (17.54 mmol) in 10 ml THE added. The mixture was warmed to ambient temperature, stirred 2 hours, then partitioned between 200 ml diethylether and 150 ml water. The organic phase was dried, concentrated, the residue purified by flash chromatography using silica gel with EtOAc/heptane, 1 9, and the product isolated in 94% yield. MS and H-NMR data supplied. 

Monofluoresceinated peptides were synthesized by adding an equimolar concentration of FITC(I) to peptides. The reaction was adjusted to a pH of 10.3 with K2CO3 and incubated at ambient temperature overnight. The resulting reaction mixture was resolved over a P-2 column (Bio-Rad) equilibrated in 0.1 M phosphate, pH 8.0 to remove unreacted fluorescein from the peptides. Fluorescently labeled peptides were analyzed by thin layer chromatography with water saturated methyl ethyl ketone as the solvent system. 

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 ... 

To a -78 °C solution of the alkyne (1.57 g, 7.92 mmol) in THF (25 mL) was added a solution of n-BuLi (2.5 M in hexanes, 3.33 mL, 8.32 mmol). The reaction mixture was stirred for 20 min and then a solution of the Weinreb amide (3.11 g, 8.71 mmol) in THF (5 mL) was added via a cannula. The reaction was allowed to warm to 0 °C and stirred for 2 h. The reaction mixture was then re-cooled to -78 °C and treated with 0.5 N HCl (5 mL). The mixture was allowed to warm to ambient temperature and stirred for 30 min. The mixture was diluted with ether and a saturated solution of sodium bicarbonate. The aqueous layer was separated and extracted with ether (3 X 30 mL). The combined ethereal extracts were washed with brine, dried (MgSO4), filtered, and concentrated to dryness. The residue was purified by column chromatography eluting with hexanes ether (20 1) to give 3.87 g (98%) of the ketone as a clear oil. 

Reaction at the 4-position of a guaiacyl system through electrophilic substitution followed by a ring closure involving an enamine was achieved in the synthesis of 8-hydroxy-9-methoxy-4,6,11,11 a-tetrahydro-1 H-benzo[bJquinoizin-2(3H)-6-one in 68% yield from the acetal shown with methyl vinyl ketone in ether solution by interaction at ambient temperature during 24 hours (under nitrogen) followed by solvent removal and treatment with concentrated hydrochloric acid at 100 C for 30 mins (ref.72). 

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. 

Not as much work has been reported on atmospheric ketone concentrations. Acetone was present at 0.001 ppm in the air at Point Barrow, Alaska (Cavanagh et al., 1969) and also, at half that concentration or less, in air over the Atlantic (Penkett, 1982 Zhou and Mopper, 1990) it is also present at higher elevations (Arnold et al., 1986). Phenyl and higher cyclic ketones, a few Cg-Cig aliphatic ketones, butanone, biacetyl and 4-methyl-2-pentanone have also been identified in ambient air (Kawamura and Kaplan, 1983 Ramdahl, 1983 Zhou and Mopper,... 

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