Ketones measurement

We can provide the following summary for the decay behavior of simple aliphatic aldehydes and ketones with little or no vibrational excitation energy on the Sp manifold under "isolated" molecule conditions at room temperature. A typical fluorescence decay time (tp) measured by a single-photon time-correlated lifetime apparatus (248) is 2-5 ns (42,101,102). A typical fluorescence quantum yield (fluorescence excitation spectroscopy is 10-, but the value is somewhat lower for aliphatic aldehydes (101,102). These values indicate that the radiative process (kp) is lO -lO s-1, three orders of magnitude slower than the total rate of nonradiative processes (kpjp) of 10 10 s-1. A typical radiative lifetime (tr) is 0.1 0.5 ps for aliphatic aldehydes and 0.1 ps for aliphatic ketones. 

A value E 12.4 1.5kcal mole" was obtained. Since this value Is comparable with the values of energy barriers to rotation observed for aromatic ketones (measured In a polystyrene matrix) which also show loss maxima around SxlO Hz, It Is... 

Preliminary experiments carried out in buffered solutions indicated that the elimination reaction takes place with a measurable rate only above a certain pH-value. The concentration of a,j8-unsaturated ketone measured at various pH-values above this value increased first with... 

Gagosian R.B., Smith S.O., Nigrelli G.E. (1982)Vertical transport of steroid alcohols and ketones measured in a sediment trap experiment in the equatorial Atlantic Ocean. Geochim. Cosmochim.Acta 46, 1163—72. 

It is evident that the rate constants of ozone interaction with ketone, measured by the static method (Fig. 6) through mixing of ozone and ketone solutions at [K] [03] are higher than those found by the bubbling method (Table 6). This is not difficult to explain because in the former case the obtained values represent the total effective constant of interaction of both the enol and the keto form. 

Misra S, Oliver NS. Utility of Ketone Measurement in the Prevention, Diagnosis and Management of Diabetic Ketoacidosis. Diabet. Med. 2015 32 14-23. http //dx.doi. org/10.1111/dme. 12604. 

Protonation equilibria of 5-substituted di(2-thienyl) ketones, measured in aqueous sulfuric acid, have been compared with those of the corresponding methyl and phenyl 2-thienyl ketones. 

Bronsted exponents for the ionization of a series of nitroalkanes and ketones, measured mainly by Bell and his collaborators [48, 55], are shown in Table 6. Although a common set of bases was not used in all cases, the bases were confined to carboxylate anions. The values are compared with isotope effects determined for ionization of the substrates with H2O as the base [48,55], and it is apparent that kff/ko increases steadily with )8, with only ethyl acetoacetate and acetylcyclohexanone out of line, and that the correlation with p is better than that with either the reactivity or pK of the substrate. The isotope effects are rather small because water is a weak base and in most cases the transition states should be strongly asymmetric in structure. Moreover because )8 refers to the much stronger carboxylate anions the absence of an isotope maximum at a = 0.5 is not surprising [48]. As would be expected, available measurements for carboxylate anions give large values of k k, but the results are too fragmentary to permit any further conclusion. 

The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

Kinetic measurements were performed employii UV-vis spectroscopy (Perkin Elmer "K2, X5 or 12 spectrophotometer) using quartz cuvettes of 1 cm pathlength at 25 0.1 C. Second-order rate constants of the reaction of methyl vinyl ketone (4.8) with cyclopentadiene (4.6) were determined from the pseudo-first-order rate constants obtained by followirg the absorption of 4.6 at 253-260 nm in the presence of an excess of 4.8. Typical concentrations were [4.8] = 18 mM and [4.6] = 0.1 mM. In order to ensure rapid dissolution of 4.6, this compound was added from a stock solution of 5.0 )j1 in 2.00 g of 1-propanol. In order to prevent evaporation of the extremely volatile 4.6, the cuvettes were filled almost completely and sealed carefully. The water used for the experiments with MeReOj was degassed by purging with argon for 0.5 hours prior to the measurements. All rate constants were reproducible to within 3%. 

Bhatnagar and Biswast measured the turbidity at 436 nm of 2l single sample of poly(methyl methacrylate) in several solvents, including acetone and methyl ethyl ketone (MEK) ... 

Eigure 2 shows that even materials which are rather resistant to oxidation ( 2/ 1 0.1) are consumed to a noticeable degree at high conversions. Also the use of plug-flow or batch reactors can offer a measurable improvement in efficiencies in comparison with back-mixed reactors. Intermediates that cooxidize about as readily as the feed hydrocarbon (eg, ketones with similar stmcture) can be produced in perhaps reasonable efficiencies but, except at very low conversions, are subject to considerable loss through oxidation. They may be suitable coproducts if they are also precursors to more oxidation-resistant desirable materials. Intermediates which oxidize relatively rapidly (/ 2 / i — 3-50 eg, alcohols and aldehydes) are difficult to produce in appreciable amounts, even in batch or plug-flow reactors. Indeed, for = 50, to isolate 90% or more of the intermediate made, the conversion must... 

Health and Safety Factors. MEK is slightly more toxic than acetone, but is not considered highly toxic, and nor does it exhibit cumulative toxicological properties. The OSHA time weighted average iu air is 200 ppm other measured toxicity values are shown iu Table 3. Methyl ethyl ketone is highly flammable. 

Low temperature filtration (qv) is a common final refining step to remove paraffin wax in order to lower the pour point of the oil (14). As an alternative to traditional filtration aided by a propane or methyl ethyl ketone solvent, catalytic hydrodewaxing cracks the wax molecules which are then removed as lower boiling products. Finished lubricating oils are then made by blending these refined stocks to the desired viscosity, followed by introducing additives needed to provide the required performance. Table 3 Usts properties of typical commercial petroleum oils. Methods for measuring these properties are available from the ASTM (10). 

Yields of excited states from 1,2-dioxetane decomposition have been determined by two methods. Using a photochemical method (17,18) excited acetone from TMD is trapped with /n j -l,2-dicyanoethylene (DCE). Triplet acetone gives i7j -l,2-dicyanoethylene with DCE, whereas singlet acetone gives 2,2-dimethyl-3,4-dicyanooxetane. By measuring the yields of these two products the yields of the two acetone excited states could be determined. The yields of triplet ketone (6) from dioxetanes are determined with a similar technique. 

AH ahphatic aldehydes and most ketones react to form cyanohydrins. The lower reactivity of ketones, relative to aldehydes, is attributed to a combination of electron-donating effects and increased steric hindrance of the second alkyl group in the ketones. The magnitude of the equiUbrium constants for the addition of hydrogen cyanide to a carbonyl group is a measure of the stabiUty of the cyanohydrin relative to the carbonyl compound plus hydrogen cyanide ... 

Equilibrium constants measured at 20—25°C, except isopropyl /-butyl ketone which was measured at 35°C. 

The anomalous effect of the last two rubbers in the table with their low solubility parameters is possibly explained by specific interaction of PVC with carbonyl and carboxyl groups present respectively in the ketone- and fumarate-containing rubbers to give a more than expected measure of compatibility. It is important to note that variation of the monomer ratios in the copolymers and terpolymers by causing changes in the solubility parameter and eompatibility will result in variation in their effect on impact strength. 

Another technique is to measure the rate of halogenation of the carbonyl compound. Ketones and aldehydes in their carbonyl forms do not react rapidly with the halogens, but the enolate is rapidly attacked. The rate of halogenation is therefore a measure of the rate of deprotonation. 

Rates of enolization can be measured in several wt s. One method involves determining the rate of halogenation of the ketone. In the presence of a sufficient concentration of bromine or iodine, halogenation is much faster than enolu ation or its reverse and can therefore serve to measure the rate of enolization ... 

Residual aromatic ether concentrations are determined from the absorbance at 278 mfi of the crude reduction products in methanol solution. Steroidal ether concentrations of 1 mg/ml are employed. The content of 1,4-dihydro compound is determined, when possible, by hydrolysis to the a, -unsaturated ketone followed by ultraviolet analysis. A solution of the crude reaction product (usually 0.01 mg/ml cone) in methanol containing about 1/15 its volume of water and concentrated hydrochloric acid respectively is kept at room temperature for 2 to 4 hr. The absorbance at ca. 240 mfi is measured and, from this, the content of 1,4-dihydro compound can be calculated. Longer hydrolysis times do not increase the absorbance at 240 mp.. 

This approach has been useful in obtaining C-1 oxygenated steroids and rather inaccessible 15-keto compounds. 16a-Hydroxy-A °kpi-egnanes have been obtained from the readily available 16a,17a-epoxy-20-ketones It has been shown °° that the product is a mixture of comparable amounts of the cis- and /ran -isomers (145,146), the structures of which were assigned on the basis of NMR measurements (ref. 200, see also ref. 306). 

The NMR study of steroidal epoxides (discussed in section II-F) parallels that of the analogous thiiranes. It is possible to relate the location and configuration of the thiirane group with the angular methyl and thiirane proton resonances. The proton NMR relationships for the intermediate thiocyanatohydrins have been included inageneral NMR study of steroids. Electronic spectra may be used in the analysis of steroidal thiiranes. Spectroscopic measurements have shown the existence of a low intensity absorption in the 240-260 m region. The regular patterns of rotatory contributions of thiiranes which are comparable with those of ketones prompted an accumulation of ORD and CD data for steroidal thiiranes. 

In addition to the expected 2,2-dimethyl- and 2a-methyl- compounds (7) and (8) the 2 -methyl-3-ketone (9) is obtained. Chemical evidence and optical rotatory dispersion measurements indicate that ring A in (7) and (9) is in the boat conformation. 

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