Replacement by Hydrogen

Several processes are available for the removal of the phenolic group (dehydroxylation). 2-Naphthyl triflate in dimethylformamide containing triethylamine, Pd ll) acetate and triphenylphosphine, after treatment with 99% formic acid and stirring of the mixture at 60°C for 1 hour under nitrogen furnished naphthalene in 91% yield (ref.51). 

A transfer hydrogenation modification has been described of a known dehydroxylation procedure (ref.52) in which the phenyl ether with 1-chloro-2-phenyltetrazole is used. The tetrazolyl ether stirred in benzene/ethanol/water (7 3 2) with 10% Pd-C was treated dropwise with 64% aqueous hydrazine, with TLC monitoring for completion of reaction, to give naphthalene in 82% yield (ref.53). 

Both these procedures are depicted in the following scheme. 

A superior method was used for the dehydroxylation of estrone in 96% yield by initial reaction with 3-chloro-1,2-benzoisothiazole-1,1-dioxide (RCI) in refluxing toluene containing triethylamine (yield 100%) followed by heating in benzene with aqueous sodium hypophosphite for 15 minutes in the presence of 10% Pd-C (ref.54). 

Trans-7,8-dihydroxy-7,8-dihydrobenzo[aJpyrene under basic conditions with tetrabutyt- ammonium hydroxide in methanol foibwed by evaporatbn at 61 under nitrogen gave an 89% yield of the 8-hydroxy compound while in methanolic phosphoric acid the 7-hydroxy compound resulted in 97% yield presumably due to the more stable allylic carbocatbn formed under these conditions while the more acidic benzyl group favoured the 8-isomer (ref.57). 

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The diazonium group may be replaced by hydrogen, thus effecting the removal of the primary amino group, deamination, by the following methods ... 

In aqueous solution intermolecular association between carboxylic acid molecules IS replaced by hydrogen bonding to water The solubility properties of carboxylic acids are similar to those of alcohols Carboxylic acids of four carbon atoms or fewer are mis cible with water m all proportions... 

Reductive deamination of primary arylamines The ammo substituent of an arylamine can be replaced by hydrogen by treatment of its de rived diazonium salt with ethanol or with hypophosphorous acid... 

A commonplace variation on the general pattern seen m carbohydrate structure is the replacement of one or more of the hydroxyl substituents by some other atom or group In deoxy sugars the hydroxyl group is replaced by hydrogen Two examples of deoxy sugars are 2 deoxy d nbose and l rhamnose... 

Also present in the first test tube is a synthetic analog of ATP in which both the 2 and 3 hydroxyl groups have been replaced by hydrogens This compound is called 2 3 dideoxyadenosme triphosphate (ddATP) Similarly ddTTP is added to the second tube ddGTP to the third and ddCTP to the fourth Each tube also contains a primer The primer is a short section of the complementary DNA strand which has been labeled with a radioactive isotope of phosphorus ( P) When the electrophoresis gel is examined at the end of the experiment the positions of the DNAs formed by chain extension of the primer are located by a technique called autoradiography which detects the particles emitted by the P isotope... 

Organochlorosilanes containing Si—H disproportionate in the presence of aluminum chloride without addition of more organosilane. Organic groups can be replaced by hydrogen (157). For example, tetraphenylsdane [1048-08-4] can be made from phenylmethylsilane [766-08-5]. 

The most useful syntheses of pyridazines and their alkyl and other derivatives begins with the reaction between maleic anhydride and hydrazine to give maleic hydrazide. This is further transformed into 3,6-dichloropyridazine which is amenable to nucleophilic substitution of one or both halogen atoms alternatively, the halogen(s) can be replaced by hydrogen as shown in Scheme 110. In this manner a great number of pyridazine derivatives are prepared. 

Alkylthio groups are oxidized to sulfoxides by H2O2 and readily by various oxidizing reagents to sulfones, e.g. in the imidazole series. The SR group is replaced by hydrogen with Raney nickel, and dealkylation is possible, e.g. of 3-alkylthio-l,2-dithiolyliums to give... 

TV-Amino groups are replaced by hydrogen on treatment with nitrous acid (e.g. 562 -> 563) (80AHC(27)24l) or phosphorus trichloride (l,2,4-triazole-4-acylimines are converted into triazoles (74AHC(17)213)). 

Gem-nitro Lmidd2Qlyl ilkdnes undergo Spj l reacdons with the anion of various nitroalkanes, as shown in Eq 5 36 The nitro group is replaced by hydrogen in 80-90% yield oi with Bn-vSnH fsee Chapter 7, which discusses radicM denitradoni... 

The nitro groups in Eqs 7 88-7 90 are readily replaced by hydrogen with dn hydndeunder radical condidons as discussed already However, the nitro groups in the ct-nitrosulfides or fi-nitrosulfides are not replaced by hydrogen on treatment with dn hydnde but the reacdon affords desulfonated products fEq 7 51 and alkenes fEq 7 97 such radical eliminadon e disaissed in Secdon 7 3 1 fsee Eqs 7 91 and 7 93 ... 

The rutro groups of a- or fi-nitrosulfides are cleanly replaced by hydrogen via ionic hydrogenation to give sulfides, as shown in Eqs 7 93-7 95 The attack of hydnde takes place at the mote subsdnited carbon... 

Carbon tetrachloride, CCU, is another molecule that, like BeF is nonpolar despite the presence of polar bonds. Each of its four bonds is a dipole, C - — CL However because the four bonds are arranged symmetrically around the carbon atom, they canceL As a result, the molecule has no net dipole it is nonpolar. If one of the Cl atoms in CCI4 is replaced by hydrogen, the situation changes. In the CHCl3 molecule, the H - — C dipole does not cancel with the three C -)— Cl dipoles. Hence CHC13 is polar. 

In a related series of experiments, the amino group and/or the carboxylic acid group of tyrosine were replaced by hydrogen atoms. The corresponding tyrosine derivatives are 3-(4 -hydroxyphenyl)-propionic acid, commonly known as desaminotyrosine (Dat), and tyramine (Tym) (structures 3-5). 

This chapter lists hydrogenolysis and related reactions by which functional groups are replaced by hydrogen e.g. RCH2X RCH2-H or R-H. 

Allomerized chlorophylls are oxidized compounds at C-13, forming theC-13 OH-chlorophyU catabolites. Other common positions for modifications and/or oxidation have been found at C-3, C-7, and C-8. Pyroderivatives of chlorophylls and their degradation products, usually found in heated and processed vegetables, lack the carbomethoxy group (-COOCH3) at C-13 of ring E, which is replaced by hydrogen. 

Reduction in which a halogen atom is replaced by hydrogen including dehalorespiration... 

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