Esters characterization

These double-base propellants are best known as smokeless propellants used in guns and rockets. Two major ingredients are used to formulate the double-base propellant grains NG and NG. As covered in Section 4.2.2, NG is a nitrate ester characterized by -O-NO2 groups, and is known as a high explosive. Since NG is a liquid at room temperature, it is absorbed by NG and serves to gelatinize the latter to form... 

Finally, the combined voltammetric and on-line differential electrochemical mass spectrometry measnrements allow a quantitative approach of the ethanol oxidation reaction, giving the partial current efficiency for each product, the total number of exchanged electrons and the global product yields of the reaction. But, it is first necessary to elucidate the reaction mechanism in order to propose a coherent analysis of the DBMS results. In the example exposed previously, it is necessary to state on the reaction products in order to evaluate the data relative to acetic acid production which cannot be directly detected by DBMS measurements. However, experiments carried out at high ethanol concentration (0.5 mol L" ) confirmed the presence of the ethyl acetate ester characterized by the presence of fragments at m/z = 61, 73 and 88 at ratios typical of the ethyl acetate mass spectrum. " This ethyl acetate ester is formed by the following chemical reaction between the electrochemically formed acetic acid and ethanol (Bq. 29) and confirms the formation of acetic acid. 

CAS 55-91-4. [(CH3)2CHO]2POF. Oily liquid, forms hydrogen fluoride in the presence of moisture. One member of a series of compounds, the fluorophosphate alkyl esters, characterized by extremely high toxicity, marked mitotic effects noted even in concentrations that are chemically undetectable. 

In a later study, the aroma constituents of a Bavarian (Pilsener) beer brewed in Hallertau, near Munich, which possessed a desirable fine hop aroma, was examined [58]. Neither the terpenes and sesquiterpenes nor the methyl esters characterized in hop oil were detected but fraction IV (Table 13.6), which contained terpenoids and sesquiterpenoids, possessed an intensive pleasant hoppy odour. Noteworthy amongst the identified constituents are the cyclic ethers (80)-(86) first found in Japanese hops, the flowery notes of which contribute to hop aroma, and the sesquiterpenoids derived from humulene such as humulene epoxide I, humulene epoxide II, humulol, and humulenol II. Similar results were found with American beers [60, 86]. Humuladienone (79)... 

Cellulose esters characterize stiffness, moderate heat resistance, high moisture vapor transmission, grease resistance, clarity and appearance, and moderate impact resistance [47],... 

Spassky, N., Simic, V., Hubert-Pfalzgraf, G., and Montaudo, M. S. (1999). Synthesis of Aliphatic Polyesters by Controlled Ring-Opening Polymerization of Cyclic Esters. Characterization, Properties, Transesterification Reactions, MacrolSymp., 144, 257-268... 

Section 20 21 Acyl chlorides anhydrides esters and amides all show a strong band for C=0 stretching m the infrared The range extends from about 1820 cm (acyl chlorides) to 1690 cm (amides) Their NMR spectra are characterized by a peak near 8 180 for the carbonyl carbon H NMR spectroscopy is useful for distinguishing between the groups R and R m esters (RCO2R ) The protons on the carbon bonded to O m R appear at lower field (less shielded) than those on the carbon bonded to C=0... 

Wax (Section 26 5) A mixture of water repellent substances that form a protective coating on the leaves of plants the fur of animals and the feathers of birds among other things A principal component of a wax is often an ester in which both the acyl portion and the alkyl portion are characterized by long carbon chains... 

Animal fats and vegetable oils are triacylglycerols, or triesters, formed from the reaction of glycerol (1,2, 3-propanetriol) with three long-chain fatty acids. One of the methods used to characterize a fat or an oil is a determination of its saponification number. When treated with boiling aqueous KOH, an ester is saponified into the parent alcohol and fatty acids (as carboxylate ions). The saponification number is the number of milligrams of KOH required to saponify 1.000 g of the fat or oil. In a typical analysis, a 2.085-g sample of butter is added to 25.00 ml of 0.5131 M KOH. After saponification is complete, the excess KOH is back titrated with 10.26 ml of0.5000 M HCl. What is the saponification number for this sample of butter ... 

The toxicity of common acryhc monomers has been characterized in animal studies using a variety of exposure routes. Toxicity varies with level, frequency, duration, and route of exposure. The simple higher esters of acryhc acid are usually less absorbed and less toxic than lower esters. In general, acrylates are more toxic than methacrylates. Data appear in Table 5. 

Bulk Polymerization. The bulk polymerization of acryUc monomers is characterized by a rapid acceleration in the rate and the formation of a cross-linked insoluble network polymer at low conversion (90,91). Such network polymers are thought to form by a chain-transfer mechanism involving abstraction of the hydrogen alpha to the ester carbonyl in a polymer chain followed by growth of a branch radical. Ultimately, two of these branch radicals combine (91). Commercially, the bulk polymerization of acryUc monomers is of limited importance. 

The physical properties of the monomers must be discussed along with those of the cured polymers because consideration of one without the other presents an incomplete picture. The 2-cyanoacryhc ester monomers are all thin, water-clear Hquids with viscosities of 1 3 mPa-s(=cP). Although a number of the esters have been prepared and characterized, only a relative few are of any significant commercial interest, and, of those, the methyl and ethyl esters by far predominate. The physical properties of the principal monomers are included in Table 1. 

Fluorinated Acids. This class of compounds is characterized by the strength of the fluorocarbon acids, eg, CF COOH, approaching that of mineral acids. This property results from the strong inductive effect of fluorine and is markedly less when the fluorocarbon group is moved away from the carbonyl group. Generally, their reactions are similar to organic acids and they find apphcations, particularly trifluoroacetic acid [76-05-1] and its anhydride [407-25-0] as promotors in the preparation of esters and ketones and in nitration reactions. 

Generally speaking, lavandin oil is characterized by a lower quantity of esters, the most critical of which for odor quaUty is linalyl acetate (24). The French specification organization (AFNOR) has fixed provisional standards for both oils (17) (Table 6). 

ROOC—COOH, are not. The dialkyl esters are characterized by good solvent properties and serve as starting materials in the synthesis of many organic compounds, such as pharmaceuticals, agrochemicals, and fine chemicals (qv). Among the diesters, dimethyl, diethyl, and di- -butyl oxalates are industrially important. Their physical properties are given in Table 7. 

The ester linkage in the repeating unit characterizes polyesters. R and R represent portions of the monomer molecule that do not participate in the polymerization. They may vary widely, giving rise to many different polyesters. Poly(ethylene terephthalate) (PET), made from ethylene glycol... 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

In humans, thiamine is both actively and passively absorbed to a limited level in the intestines, is transported as the free vitamin, is then taken up in actively metabolizing tissues, and is converted to the phosphate esters via ubiquitous thiamine kinases. During thiamine deficiency all tissues stores are readily mobilhed. Because depletion of thiamine levels in erythrocytes parallels that of other tissues, erythrocyte thiamine levels ate used to quantitate severity of the deficiency. As deficiency progresses, thiamine becomes indetectable in the urine, the primary excretory route for this vitamin and its metaboHtes. Six major metaboHtes, of more than 20 total, have been characterized from human urine, including thiamine fragments (7,8), and the corresponding carboxyHc acids (1,37,38). 

Infrared Spectroscopy (ir). Infrared curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxyflc acids, alcohols, and esters. The ir curves are typically used in combination with other analytical methods such as dsc or gc/gpc to characterize waxes. 

Thin-layer chromatography (76,77) has been used for the estimation of the amounts of dimer, trimer, and monomer ia methyl esters. Both this method and paper chromatography are characterized by lack of precision (78,79) (see Chromatography). 

Oils are mixtures of mixed esters with different fatty acids distributed among the ester molecules. Generally, identification of specific esters is not attempted instead the oils are characterized by analysis of the fatty acid composition (8,9). The principal methods have been gas—Hquid and high performance Hquid chromatographic separation of the methyl esters of the fatty acids obtained by transesterification of the oils. Mass spectrometry and nmr are used to identify the individual esters. It has been reported that the free fatty acids obtained by hydrolysis can be separated with equal accuracy by high performance Hquid chromatography (10). A review of the identification and deterrnination of the various mixed triglycerides is available (11). 

In addition, glycidyl esters are produced by the reaction of cycloahphatic carboxyUc acids with epichlorohydrin, followed by dehydrohalogenation with caustic. Such products are characterized by low viscosities (ca 500 mPa-s (=cP)). Reactivity of the glycidyl esters more closely resembles the standard bisphenol—epichlorohydrin resins. 

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