Acid OH groups

Orthophosphoric acid containing three acid OH groups in the molecule offers many opportunities for the realization of surface-active molecular structures. But phosphoric acid also possesses the ability to form polyacids in an widespread manner. Pyrophophoric acid and triphosphoric acid are substances that have been known for a long time. This presents further possibilities for interesting synthesis. 

Fig. 3 shows the IR spectra of the adsorbed species generated on the surface in the presence of both Hj and Oj at different temperatures. No obvious absorption band due to the adsorbed species was observed at 298 K. When the temperature was increased to 473 K, tw o weak bands at 3740 and 3670 cm assigned to the stretching vibrations of a non-acidic and acidic OH groups, respectively, were observed. These two bands were also observed in H,... 

Metal alkyl reagents react with the acidic OH groups of silica, probably by the electrophilic cleavage of the metal-carbon bond. For example, the electrophilic cleavage of the metal-carbon bond occurs when organometallic reagents react with the electrophilic OH groups of the silica surface (Scheme... 

The surfaces of some types of silica and alumina freed from adsorbed water contain acidic -OH groups. Ballard et al. (15) showed that these -OH groups react readily with transition metal alkyls giving stable compounds that are highly active polymerization catalysts for olefins. These systems are best described with reference to silica. 

Figure 4.34 Position of IR band (due to acidic OH groups) with respect to varying Si/AI ratios in different zeolites. (Reprinted from Introduction to Zeolite Science and Practice, Studies in Surface Science and Catalysis, Vol. 58, J.H.C. van Hooff, J.W. Roelofsen, Techniques of Zeolite Characterization, pp. 241-283. Copyright 1991. With permission from Elsevier.)...

Small amounts of these acids or other phosphorus compounds containing acidic OH groups inhibit the SSP process. This inhibition of Ti-catalyzed polycondensation is related to the formation of stable adducts between the acidic phosphorus compound and the catalyst [53], Such a problem can be overcome by the use of certain compounds, for example, nonyl phosphite, in exact, equivalent amounts [54],... 

Simultaneously, anchored subcarbonylic species can be generated by slightly acidic OH groups [104]. 

The band centered at 3615 cm disappears by adsorption of pyridine and further outgassing at 150°C, thus confirming its assignment to stretching vibration of acidic OH groups. For samples with a different Si/Al ratio, a direct correlation is observed between the intensity of this band and that of protonated pyridine at 1540 cm (Table I). 

In addition, Pauling and Sherman (222) had proposed a ring structure for the anion of aluminium tetrametaphosphate on the basis of a crystal structure determination. The triphosphate NaBP3Oi0 must, then, have the chain structure already proposed by Schwarz (263), for Rudy and Schloesser (250) showed that the acid corresponding to the triphosphate has three strongly and two weakly acidic OH groups with the weakly acidic groups... 

The free acids carry a strongly dissociated acid OH group on each phosphorus atom and each of the two ends of the chain has a weakly dissociated... 

HOCHjCHjCl cannot be converted directly to the Grignard because of the presence of the acidic OH group the product obtained would be HOCHjCH,. The desired reaction is achieved by protecting the OH group as shown schematically ... 

Phenolic There are various kinds of phenolic resins. The ones that are produced from phenol-formaldehyde condensation are veiy weak acid exchangers, where the phenolic -OH groups are the fixed-ionic groups. The formaldehyde content decides the extent of cross-linking in the resin. On the other hand, phenolsulfonic acid resins contain both strong acid -S03H and weak acid -OH groups. 

It is often used for the rapid and quanhtative methylahon of acidic OH groups... 

The proton originates from acidic OH-groups of the catalyst surface. The importance of acidic sites is stressed by several authors [11,141,312] of whom Takita et al. [312] have demonstrated a linear relationship between activity and the concentration of acidic sites in the case of a Sn—Mo—O catalyst. Regarding the attachment of oxygen to the carbon formed, Moro-oka et al. proved by the use of H2180 together with 1602 that the introduced oxygen mainly stems from water. (It is noted that acrolein, formed as a by-product, did not contain ]80.) On this basis, the mechanism proposed by Buiten is... 

It must be additionally assumed that the acidic OH-group is regenerated by water from the gas phase, while the remaining protons react on a different site with oxygen anions and desorb as water. A significant isotope effect for the hydrogen at the second carbon atom, observed by Buiten, may indicate that the second step in the above scheme is rate-controlling. 

The restructuring of the framework in connection with the re-coordination of Al in MCM-41 is also reflected in the v(OH) vibration spectra of the calcined sample. Two vibration bands appear in the range of the vibrations of Bransted acid bridging OH groups at 3628 and 3600 cm 1 (Fig. 3). The bands are absent in the spectra of NH4-MCM-41. These bands disappear immediately after adsorption of ammonia and re-appear after ammonia desorption at 500°C. This behaviour additionally supports the assignment of these bands to acidic OH groups. The bridging hydroxyl vibration bands are well resolved and broad. After hydrothermal treatment... 

Jensen et al. 1962), have been found in milk fat. These isomers convert readily to lactones, some of which are flavor compounds. Schwartz (1972), in a discussion of methods for the isolation of nonlactonegenic hydroxy fatty acids (OH group on carbons other than 4 or 5), mentioned that there were at least 60 acids in this fraction. 

Support-bound phenols [173-176] or other compounds with an acidic OH group (oximes [177-179], hydroxamic acids, /V-hydroxy benzotriazoles, etc.) undergo rapid esterification with carbodiimides as coupling agents (Entries 13 and 14, Table 13.12). The resulting products are susceptible to nucleophilic attack, and can be used as insoluble acylating agents. 

Most of the alkyls of the other early transition metals demonstrate similar reactivity.101102 Hydridic metal hydrides will similarly react with the weakly acidic OH groups of alcohols and phenols, liberating hydrogen and forming alkoxides or phenoxides. Aluminum hydride will undergo stepwise substitution by alcohols (equation 29).103... 

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