Hydroxyl percentage

Hydroxyl percentage (%OH) is another form of expressing the concentration of hydroxyl groups in any polyol. The sum of the atomic weights in the OH groups is 16 + 1 =17 g/OH group. 

Hydroxyl percentage is defined as the gravimetric percentage of all the hydroxyl groups in an oligo-polyol molecule  

The hydroxyl percentage is easily obtained by dividing the hydroxyl number (OH ) by 33. The hydroxyl number is then calculated from the equation  

An oligo-polyol with an hydroxyl number of 56 mg KOH/g, for example, has 1.6969% hydroxyl groups and a polyol with an OH of 400 mg KOH/g has 12.12% hydroxyl groups. 

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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%. 

To conclude, the common physico-chemical characteristics of oligo-polyols for polyurethanes determined by standard analytical methods are hydroxyl number, hydroxyl percentage, primary hydroxyl content, molecular weight, equivalent weight, molecular weight distribution, viscosity, specific gravity, acidity and colour (See Chapters 3.1-3.11). 

Practical experience of many ethoxylation reactions proved that in two different reactors, with different hydrodynamic conditions, at the same EO concentration different primary hydroxyl percentages are obtained. 

In conclusion, the ethoxylation catalyst nature has an important influence on the primary hydroxyl content. A higher primary hydroxyl percentage than in the classical reaction catalysed by KOH is obtained by the ethoxylation of the intermediate polyether polyols in acidic catalysis or with alkaline-earth alkoxides or carboxylates [25-29]. 

Polyurethanes. About 3% of the U.S. polyurethanes market in 1988 was derived from the condensation product of polyisocyanates with low molecular weight polyadipates having hydroxyl end groups (195). In 1986 this amounted to 29,000 t, or 4% of total adipic acid consumption. The percentage was similar in Western Europe. About 90% of these adipic acid containing polyurethanes are used in flexible or semirigid foams and elastomers, with the remainder used in adhesives, coatings, and spandex fibers. 

It was observed that beyond optimum total dose the percentage of grafting decreased. This may be due to the fact that at higher total doses beyond optimum, chain degradation by /3-scission (reaction 35, 37, 38) occurs. Further at higher doses, hydroxyl radicals arising from... 

Fig. 3. a) First order plot of oxygen uptake in the Methylene-blue (MB)-sensitized photooxidation of GA 8.4 pM and 1.3 mM histidine (control) in phosphate buffer pH 7. b) Percentage radical scavenging activity for the control molecule Trolox and GA at pH 7.4 in phosphate buffer 10 mM (hydroxyl radical) and pH 10 in sodium carbonate buffer 50 mM (anion superoxide radical). 

Figure 18.2 Representative receiver operator curves to demonstrate the leave n out validation of K-PLS classification models (metabolite formed or not formed) derived with approximately 300 molecules and over 60 descriptors. The diagonal line represents random. The horizontal axis represents the percentage of false positives and the vertical axis the percentage of false negatives in each case. a. Al-dealkylation. b. O-dealkylation. c. Aromatic hydroxylation. d. Aliphatic hydroxylation. e. O-glucuronidation. f. O-sulfation. Data generated in collaboration with Dr. Mark Embrechts (Rensselaer Polytechnic Institute).

It is clear from the results in Table II that o-hydroxylation accounts for a major part of the metabolism of DMN vivo. The percentage is a little lower than the preliminary values obtained by Halsman, Haliday and Magee (23) > but it is... 

The relatively low percentage of ring substitution can be attributed to several side reactions 1,4-addition of Li to 2-cyclopentenone, incomplete dehydration of 4 as evidenced by the presence of a small hydroxyl absorption (3425 cm ) in the IR spectrum of 5, and reduction of the polymer-bound cyclopentadiene in its reaction with Co2(C0)8 (26,27,32). 

Figure 9.5 Percentage inhibition of 1- and 4 -hydroxylation of triazolam in the presence of varying inhibitors [220],...

Of course, all the appropriate higher-temperature reaction paths for H2 and CO discussed in the previous sections must be included. Again, note that when X is an H atom or OH radical, molecular hydrogen (H2) or water forms from reaction (3.84). As previously stated, the system is not complete because sufficient ethane forms so that its oxidation path must be a consideration. For example, in atmospheric-pressure methane-air flames, Wamatz [24, 25] has estimated that for lean stoichiometric systems about 30% of methyl radicals recombine to form ethane, and for fuel-rich systems the percentage can rise as high as 80%. Essentially, then, there are two parallel oxidation paths in the methane system one via the oxidation of methyl radicals and the other via the oxidation of ethane. Again, it is worthy of note that reaction (3.84) with hydroxyl is faster than reaction (3.44), so that early in the methane system CO accumulates later, when the CO concentration rises, it effectively competes with methane for hydroxyl radicals and the fuel consumption rate is slowed. 

In the horse, hydroxylation is more important than acetylation as a metabolic pathway, with hydroxylation at the 5 position being dominant over hydroxylation of the 6-methyl group. Low percentages of metabolites are present in plasma, for N -SDM, 0.6 to 0.9 % for SCH2OH, 0.38 to 0.71 % and for SOH, 0.38 to 6.7 %. The plasma concentration-time curves of the metabolites run parallel to that of SDM. The elimination half-life of sulfadimidine varies between 5 and 14 h. The main metabolite in urine, accounting for 50 % of the drugs present (Table III), is the SOH and its glucuronide. 

Laying-hens eliminate sulfadimidine rapidly by metabolic pathways including hydroxylation and acetylation. Following intravenous SDM administration, a biphasic elimination-time curve was noticed 10.2 + 3.3 H). Figure 8 shows the plasma disposition of SDM and its metabolites following an oral SDM bolus administration once daily of 100 mg/kg to a chicken. The percentage of N -SDM in plasma is the highest (Table I). Within 3 days of termination of the SDM therapy, plasma concentrations of SDM and its metabolites falls rapidly below the detection limit of the HPLC method (0.02 /ig/ml). 

For example, reduction of 2-alkylcycloalkanones with lithium aluminum hydride in tetrahydrofuran gave the following percentage proportions of the less stable cu-2-alkylalkanol (with axial hydroxyl) 2-methylcyclobutanol 25%, 2-methylcyclopentanol 21%, 2-methylcyclohexanol 25%, 2-methylcy-cloheptanol 73%, and 2-methylcyclooctanol 73% (the balance to 100% being the other, trans, isomer) [837. ... 

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