Hydroxyl, determination

Figure 9,9 Amounts of molecular H2O and OH hydroxyls determined in hydrated silicate glasses by IR spectroscopy. Reprinted from E. Stolper, Geochimica et Cosmochimica Acta, 46, 2609-2620, copyright 1982, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Given and coworkers studying the "British Macerals" took more of an organic chemist s approach to characterization. The macerals were subjected to solvent extraction, lithium reduction, hydroxyl determination, oxidation, and reaction with various reagents. N-bromosuccinimide (NBS) was used to bromin-ate aliphatic carbons which in the case for four macerals from an Aldwarke Silkstone coal yielded per 100 carbon atoms the following distribution of hydrogen which is replaced by bromine (61) vitrinite 16, exinite 25 1/2, micrinite 12, and fusinite... 

The method is extremely simple and needs only the neutralisation of the resulting hydrochloric acid with a strong base solution of a known concentration. Unfortunately, as mentioned previously, this method is not very accurate. The most accurate and usual methods for primary hydroxyl determination are two NMR spectroscopic methods 19fluorine NMR and 13carbon NMR. Both methods are described in detail in ASTM D4273 [34]. 

The 19fluorine NMR method is one of the most accurate methods for primary hydroxyl determination. It is suitable for oligo-polyols (especially poly ether polyols) with hydroxyl numbers in the range 24-300 mg KOH/g and primary hydroxyl percentages in the range of 2 to 98%. 

The quantitative aspect of hydroxyl determination is illustrated in Table 3.7 for the analysis of hydroxyl in some polymeric materials. In most cases, the fluorine resonance from n-h xty trifluoroacetate (at 7463 Hz in Figure 3.8) was used as internal standard to calibrate the spectral integral. From the data shown in Table 3.7, it seems that the adduct... 

V. Oxygen-Dependent Prolyl Hydroxylation Determines O2 Lability of HIF-1 ... 

The quantitative aspect of hydroxyl determination is illustrated in Table 1.16 for the analysis of hydroxyl in some polymeric materials. 

Determined from membrane osmometry. Calculated value based on the degree of hydroxylation. Determined from GPC. 

Van Oss and Good [148] have compared solubilities and interfacial tensions for a series of alcohols and their corresponding hydrocarbons to determine the free energy of hydration of the hydroxyl group they find -14 kJ/mol per —OH group. 

The analyses which follow are arranged in the order in which they would be applied to a newly discovered substance, the estimation of the elements present and molecular weight deter-minations(f.e., determination of empirical and molecular formulae respectively) coming first, then the estimation of particular groups in the molecule, and finally the estimation of special classes of organic compounds. It should be noted, however, that this systematic order differs considerably from the order of experimental difficulty of the individual analyses. Consequently many of the later macro-analyses, such as the estimation of hydroxyl groups, acetyl groups, urea, etc. may well be undertaken by elementary students, while the earlier analyses, such as estimation of elements present in the molecule, should be reserved for more senior students. 

I. DETERMINATION OF NUMBER OF HYDROXYL GROUPS IN PHENOL. CjHjOH. Molecular Weight, 94. 

DETERMINATION OF THE NUMBER OF HYDROXYL GROUPS IN (ii) GLYCOL. Molecular Weight, 62. 

The method can be used to determine the amount of a known alcohol or phenol present in a crude sample, provided that the impurities do not themselves contain hydroxyl groups. 

Vrocttd precisely as in the Determination of the Number of Hydroxyl Groups in Phenol, except that after weighing the flask A, run in about i ml. of pure aniline, and weigh again. Then continue exactly as before. The acetanilide which is formed usually remains in solution when the contents of the flask A are diluted with water for hydrolysis. 

The ultraviolet absorption spectrum of thiazole was first determined in 1955 in ethanolic solution by Leandri et al. (172), then in 1957 by Sheinker et al. (173), and in 1967 by Coltbourne et al. (174). Albert in 1957 gave the spectrum in aqueous solution at pH 5 and in acidic solution (NHCl) (175). Nonhydroxylic solvents were employed (176, 177), and the vapor-phase spectrum was also determined (123). The results summarized in Table 1-15 are homogeneous except for the first data of Leandri (172). Both bands A and B have a red shift of about 3 nm when thiazole is dissolved in hydrocarbon solvents. This red shift of band A increases when the solvent is hydroxylic and, in the case of water, especially when the solution becomes acidic and the extinction coefficient increases simultaneously. 

Hydroxyl groups take precedence over ( outrank ) alkyl groups and halogen substituents m determining the direction m which a carbon chain is numbered The OH group is assumed to be attached to C 1 of a cyclic alcohol and is not numbered... 

The chemical shift of the hydroxyl proton signal is variable depending on solvent temperature and concentration Its precise position is not particularly significant m struc ture determination Because the signals due to hydroxyl protons are not usually split by other protons m the molecule and are often rather broad they are often fairly easy to... 

This reaction has been used m an imaginative way to determine the ring size of glycosides Once all the free hydroxyl groups of a glycoside have been methylated the glycoside is subjected to acid catalyzed hydrolysis Only the anomeric methoxy group IS hydrolyzed under these conditions—another example of the ease of carbocation for matron at the anomeric position... 

Each primer is a synthetic oligonucleotide of about 20 bases prepared so that then-sequences are complementary to the (previously determined) sequences that flank the tar get regions on opposite strands Thus one primer is annealed to one strand the other to the other strand The 3 hydroxyl end of each primer points toward the target region The stage is now set for DNA synthesis to proceed from the 3 end of each primer [Figure 28 14(c )] The solution contains a DNA polymerase and Mg " m addition to the... 

The relationship between the BET monolayer capacity of physically adsorbed water and the hydroxyl content of the surface of silica has been examined by Naono and his co-workers in a systematic study, following the earlier work by Morimoto. Samples of the starting material—a silica gel—were heated for 4 hours in vacuum at a succession of temperatures ranging from 25 to 1000°C, and the surface concentration of hydroxyl groups of each sample was obtained from the further loss on ignition at 1100°C combined with the BET-nitrogen area. Two complete water isotherms were determined at 20°C on each sample, and to ensure complete... 

In Table 5.3, is compared with the total hydroxyl concentration (Ni, + N ) of the corresponding fully hydroxylated, sample. The results clearly demonstrate that the physical adsorption is determined by the total hydroxyl content of the surface, showing the adsorption to be localized. It is useful to note that the BET monolayer capacity n JH2O) (= N ) of the water calculated from the water isotherm by the BET procedure corresponds to approximately 1 molecule of water per hydroxyl group, and so provides a convenient means of estimating the hydroxyl concentration on the surface. Since the adsorption is localized, n.(H20) does not, of course, denote a close-packed layer of water molecules. Indeed, the area occupied per molecule of water is determined by the structure of the silica, and is uJH2O) 20A ... 

V, = hydroxyl content before isotherm determination (OH groups per 1(X) A ). 

The BET monolayer capacity N, calculated from the first water isotherm included both physisorbed and chemisorbed water, whereas that from the second isotherm iV, included only the physisorbed water. Thus the difference (iV, - N,) gave the amount of chemisorbed water taken up as hydroxyl groups during the isotherm determination. N, + iV ) was therefore the total concentration of hydroxyl groups on the surface when the second water isotherm was being measured. 

Thus in Fig. 5.22 the first outgassing at 25°C will have removed physisorbed water only, so that curve (1) is the isotherm of physical adsorption on the fully hydroxylated material. The 300°C outgassing, on the other hand, will have removed all the ligand water and the majority of the hydroxyl groups when isotherm (4) is determined, therefore, the Ti ions will chemisorb ligand water at low relative pressure, but the number of hydroxyl groups reformed will be very small. 

Prior to determination of an isotherm, all physisorbed material has to be removed from the surface of the adsorbent. This is best achieved by exposure of the surface to high vacuum, the exact conditions required (temperature and residual pressure) being dependent on the particular gas-solid system. In routine determinations of surface area it is generally advisable not to remove any chemisorbed species which may be present thus, the hydroxylated oxides are usually outgassed at 1S0°C. Microporous adsorbents such as zeolites or active carbons however require higher temperatures (350-400 C, say) for complete removal of physisorbed material from their narrowest pores. An outgassing period of 6-10 hours (e.g. overnight) is usually sufficient to reduce the residual pressure to 10 Torr. 

---