Phenol-assisted addition

Meyer-Dulheuer [55] has analysed the pure additives (phenolic antioxidants, benzotriazole UV stabilisers and HALS compounds) of Table 9.8 in THF solutions by means of MALDI-ToFMS. As it turns out, polar molecules in the mass range of below 800 Da, which have a high absorption coefficient at the laser wavelength used, can often be measured without any matrix [55,56]. In this case, there is no matrix-assisted laser desorption and ionisation (MALDI) process any more. It is a simple laser desorption/ionisation (LDI) process. The advantage of this method is a matrix-free mass spectrum with the same mass resolution as in the MALDI case,... 

Figure 17.2 Phenol-assisted addition and dehydration transition states in the enamine formation between pyrrolidine and propanal.

In addition to the ruthenium SNAr chemistry discussed in Section 11.7.2, an analogous copper-assisted S Ar cyclization reaction of a boronic acid and a phenol has been reported to construct biaryl ethers 146 (Scheme 11.19). Specifically, this functionality was then incorporated into MMP inhibitors. The mild conditions were shown to tolerate amides and esters in the substrate, although the presence of an additional phenol resulted in only trace product. Some other transformations involving copper mediation are presented in Section 11.8. 

Procedure. Prepare four test solutions of phenol by placing 200 mL of boiled and cooled distilled water in each of four stoppered, 500 mL bottles, and adding to each 5g of sodium chloride this assists the extraction procedure by salting out the phenol. Add respectively 5.0, 10.0, 15.0 and 20.0 mL of the standard phenol solution to the four bottles, then adjust the pH of each solution to about 5 by the careful addition of 5M hydrochloric acid (use a test-paper). Add distilled... 

The addition to a double bond is observed in aromatic substrates where the reaction is assisted by chelation. The initial success of such reactions was achieved with the double alkylation of phenol with ethene (Equation (2)).1 This reaction occurs at the or/ -positions selectively by using an orthometallated ruthenium phosphate complex 1. 

In the last years, ILs have been applied as matrices for matrix-assisted laser desorption/ionization (MALDI) MS [42], thus expanding the use of MALDI. In Ref. 38 the suitability of alkylammonium- and alkylimidazolium salts of a-cyano-4-hydroxycinnamic acid was investigated as a MALDI matrix and at the same time as the additive of BGE. The alkylammonium salt produced better separation of phenolic compounds than the alkylimidazolium salt. The investigation suggests that it is possible to synthesize ILs suitable for electrophoretic analysis as well as for online MALDI-MS analysis. 

Three types of iodothyronine deiodinase remove iodine atoms from thyroxine to form the active thyroid hormone triiodothyronine and also to inactivate the hormone by removing additional iodine531 541-546 (see also Chapter 25). In this case the - CH2- Se- may attach the iodine atom, removing it as I+ to form -CH2-Se-I. The process could be assisted by the phenolic -OH group if it were first tautomerized (Eq. 15-60). 

Phenols and Enolizable Keto Compounds. These compounds are coupled in alkaline (soda) solution as a rule. If the coupler is a sulfonic or carboxylic acid, or is soluble in water (e.g., resorcinol), it is dissolved directly in the required amount of soda solution. In other cases, the coupler is dissolved in the equivalent amount of dilute sodium hydroxide solution and the recaustic soda for complete solution in such cases, no more is used than is absolutely required. (Solution of the 2-hydroxyl-3-naphthoic acid arylides is greatly assisted by the addition of alcohol. In many cases, no other method of dissolving the coupler is known.) An unnecessarily large excess of alkali is to be avoided, except in special cases, since such an excess rapidly decomposes the diazo compound. It is desirable to use that amount of soda which will be converted to bicarbonate by the acid of... 

An additional effect, which is the most important of all the phenomena observed in these experiments, is the effect the Fe ions observe on the overall mineralization rate of phenol. The Fe not only enhances the rate of oxidation of phenol and changes the formation of its oxidation intermediates but also accelerates the rate of its overall mineralization. Figure 9a and b compare the TOC profiles for the oxidation of 20 and 30 ppm C of phenol in both impromoted PC and Fe-assisted PC systems. It can be seen that during the Fe-assisted PC reaction, the overall mineralization of phenol is faster than that for the impromoted PC reaction. One can also observe that for both cases, during the first part of the reaction time, the two profiles follow a similar trend. The TOC profile in the Fe-assisted PC systems, however, drops off faster than that in the PC system. More importantly, one can notice that in the last part of the reaction period, there is a considerable change on the slope of the TOC profile in the Fe-assisted PC reactions. 

Another instructive example of electrophilic or H-bonding assistance of protic solvents (or co-solvents) in SnI reactions is the accelerated acetolysis rate of 2-bromo-2-methylpropane upon the addition of phenols to a tetrachloromethane/acetic acid solution of the reactant [582] see reference [582] for further examples. The usefulness of phenol as a solvent for SnI solvolysis reactions, in particular phenolysis of 1-halo-l-phenylethanes, has been stressed by Okamoto [582], In spite of its low relative permittivity (fir = 9.78 at 60 °C), its low dipolarity fi = 4.8 10 Cm = 1.45 D), and its low nucleophihcity, it represents a solvent of high ionizing power due to its electrophilic driving force. 

Existing studies on the US-assisted hydrolysis of carbohydrates have failed to clarify the behaviour of chemical systems upon US irradiation [87]. Thus, Dubois et al. used a US bath at a frequency of 35 kHz — further details were not reported — as, in their opinion, a probe increases the temperature of the irradiated system significantly. They found very acid conditions (12 M sulphuric acid) to cause total degradation of carbohydrates — the sonicated solution did not exhibit any absorption at 485 nm after the addition of phenol for the development of the Dubois method [88]. They concluded that promoting hydrolysis in an acid medium — it is unclear whether they assayed different acid concentrations — is not feasible and performed the ultrasonicated hydrolysis step in pure water for 3 h, after which they added the acid to develop the derivatizing reaction. Further research on this topic is clearly required in order to clarify such an uncommon behaviour. 

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