Phenohc proton

The photochemistry of sahcyhdeneanUmes suffers from competing reversible photoreactions involving transfer of the phenohc proton to the imino nitrogen, along with the formation of the corresponding o-quinoid forms (photochromism) or a zwitterion. ... 

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

Chemical off—on switching of the chemiluminescence of a 1,2-dioxetane (9-benzyhdene-10-methylacridan-l,2-dioxetane [66762-83-2] (9)) was first described in 1980 (33). No chemiluminescence was observed when excess acetic acid was added to (9) but chemiluminescence was recovered when triethylamine was added. The off—on switching was attributed to reversible protonation of the nitrogen lone pair and modulation of chemically induced electron-exchange luminescence (CIEEL). Base-induced decomposition of a 1,2-dioxetane of 2-phen5l-3-(4 -hydroxyphenyl)-l,4-dioxetane (10) by deprotonation of the phenoHc hydroxy group has also been described (34). 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

The symbols f and f correspond to total fraction of and hybridi2ed carbon, respectively, f represents the fraction of carbon in aromatic rings f , the fraction in carbonyls, b > 165 ppm the aromatic fraction that is protonated the aromatic fraction that is nonprotonated f, the phenoHc or phenohc ether carbon, 6 = 150-165 ppm f, the alkylated aromatic carbon, 6 = 135-150 ppm , the aromatic bridgehead carbon f represents the fraction of CH or CH2 aUphatic carbon f, the CH or nonprotonated aUphatic carbon and f, the aUphatic carbon bound to oxygen, b — 50-90 ppm. 

Dissociation extraction is the process of using chemical reaction to force a solute to transfer from one liquid phase to another. One example is the use of a sodium hydroxide solution to extract phenohcs, acids, or mercaptans from a hyclrocarbon stream. The opposite transfer can be forced by adding an acid to a sodium phenate stream to spring the phenolic back to a free phenol that can be extracted into an organic solvent. Similarly, primary, secondary, and tertiary amines can be protonated with a strong acid to transfer the amine into a water solution, for example, as an amine hydrochloride salt. Conversely, a strong base can be added to convert the amine salt back to free base, which can be extracted into a solvent. This procedure is quite common in pharmaceutical production. 

Proton transfer also arises from phenohc gronps to the nitrogen of several heterocyclic componnds. Thus the pyridine derivative 24 shows photochemical proton transfer and the influence of restricted rotation on the process was assessed using the locked derivatives 25 and 26 . Proton transfer is also observed in [2,2 -bipyridyl]-3,3 -diol and within the anil of hydroxyindanone . Benzimidazole derivatives such as 27, X = also undergo... 

In fact, the proton on nitrogen is slightly more acidic than the phenohc hydroxyl, as measured by the values of the following model compounds ... 

Brust and coworkers studied chemical reactivity of thiol-capped gold colloids. A colloid modified with p-mercaptothiophenol is soluble in ethyl acetate. It can, however, be transferred into alkahne aqueous phase due to deprotonation of the phenolic groups. Acidification of the system effects protonation of phenolates and transfer of the colloid back to the aqueous phase" . Exposure of the above coUoid to propionic anhydride leads to partial esterification. That phenohc groups, however, remain intact was attributed to steric hindrance. 

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