RoHS Basics

The dimethylplatinum(II) complexes having chelate nitrogen ligands, [PtMe2(N-N)] (N-N = 2,2 -bipyridyl or 1,10-phenanthroline) (46) reacted with alcohols (ROH, R = Me, Et, Pr) to give hygroscopic and basic platinum(IV) complexes. 

In solutions with relatively high ammonia concentrations, NH3 reacts with NP to give Fe(CN)5(H20)3 plus N2, effecting comproportionation of NH3 and NO+ to N2 (60,52c). Likewise, primary amines (RNH2) are diazotized by aqueous NP to give the alcohols (ROH) plus N2, with the maximum rate occurring about pH 10.5 (55). The rates of these reactions are first-order in [NP] and [RNH2] and increase with the basicity of the amines. 

Also other Type B and C series from Table II are consistent with the above elimination mechanisms. The dehydration rate of the alcohols ROH on an acid clay (series 16) increased with the calculated inductive effect of the group R. For the dehydrochlorination of polychloroethanes on basic catalysts (series 20), the rate could be correlated with a quantum-chemical reactivity index, namely the delocalizability of the hydrogen atoms by a nucleophilic attack similar indices for a radical or electrophilic attack on the chlorine atoms did not fit the data. The rates of alkylbenzene cracking on silica-alumina catalysts have been correlated with the enthalpies of formation of the corresponding alkylcarbonium ions (series 24). Similar correlations have been obtained for the dehydrosulfidation of alkanethiols and dialkyl sulfides on silica-alumina (series 36 and 37) in these cases, correlation by the Taft equation is also possible. The rate of cracking of 1,1-diarylethanes increased with the increasing basicity of the reactants (series 33). 

Problem 6.14 (a) Suggest a mechanism for the dehydration of CH,CHOHCH, that proceeds through a carbocation intermediate. Assign a catalytic role to the acid and keep in mind that the O in ROH is a basic site like the O in H,0. (b) Select the slow rate-determining step and justify your choice, (c) Use transition states to explain the order of reactivity of ROH 3°>2°> 1°. <... 

Alcohols are basic enough to accept a proton from strong acids, e.g. HCl and H2SO4, and able to dissociate completely in acidic solution. Sterically hindered alcohols, e.g. tert-butyl alcohol, are strongly basic (higher pA a values), and react with strong acids to give oxonium ions (ROH+). 

For substitution at a carbonyl carbon, the nucleophilicity order is not the same as it is at a saturated carbon, but follows the basicity order more closely. The reason is presumably that the carbonyl carbon, with its partial positive charge, resembles a proton more than does the carbon at a saturated center. That is, a carbonyl carbon is a much harder acid than a saturated carbon. The following nucleophilicity order for these substrates has been de-termmined 321 Me2C=NO- > EtO" > MeO > OH" > OAr- > N-f > F" > H20 > Br" I". Soft bases are ineffective at a carbonyl carbon.322 In a reaction carried out in the gas phase with alkoxide nucleophiles OR solvated by only one molecule of an alcohol R OH, it was found that both RO and R O" attacked the formate substrate (HCOOR") about equally, though in the unsolvated case, the more basic alkoxide is the better nucleophile.323 In this study, the product ion R"0 was also solvated by one molecule of ROH or R OH. 

The absorption and emission spectra of 10-CPT in water-methanol mixtures at room temperature (ca. 22 °C) in the pH range from neutral to basic in general exhibit a well-known naphthol-type behavior [4]. The absorption spectra in neutral water and methanol are nearly identical, the latter having a 3 nm bathochromic shift. The equilibrium between neutral (ROH, 380 nm) and Odeprotonated (RO, 420 nm) forms of 10-CPT is characterized by a pof 8.9 in a 68% mole H2O mixture (Fig. 1 right). The protonation of quinolinium nitrogen has a pKa of around 1.0, more than 3 pK units lower than the parent 6HQ. 

A good example of the use of the functional-group concept is for acid-base properties. Alcohols, ROH, are structurally related to water, HOH, in that both possess a hydroxyl function. We may then expect the chemistry of alcohols to be similar to that of water. In fact, both are weak acids because the OH group has a reactive proton that it can donate to a sufficiently strongly basic substance, written as B here ... 

As you read the chapter you will recognize a similarity between the chemistry of amines and the chemistry of alcohols, which we discussed in Chapter 15. Primary amines (RNH2) and secondary amines (R2NH) are much weaker acids than alcohols (ROH) and form strongly basic anions ... 

The oxygen and sulfur bases are weaker than the nitrogen bases, and accurate solution basicities are not available. Arnett s heat of protonation studies indicate that the order of decreasing basicity is ROR > ROH > HaO,98 a result that is in agreement with gas-phase measurements.99 Hydrogen sulfide in the gas phase has basicity comparable to that of water (Table 3.18), and substitution of H by alkyl produces stronger gas-phase bases just as does similar substitution on oxygen. 

Buffer catalysis of the hydrolysis of phenyl (311 R = Ph) and methyl (311 R = Me) benzenesulfinates to give the sulfinic acid (312) and alcohol ROH is strongly accelerated by both carboxylate and amine components of the buffer which give Bronsted /i values of approximately unity on separate lines. The carboxylates are about 44 tunes more effective than amines of similar basicity. A concerted. S n2 mechanism with a hypervalent intermediate (313) is proposed for the nucleophilic reaction of these esters.286 The reaction of the thiosulfinate esters (314) with sulfenyl chlorides RSCI and sulfenate esters (315) to give sulfinyl chlorides and disulfides and sulfinate esters and disulfides, respectively, has been studied.287 Hydrolysis of 2-(3-aminophenyl)sulfonyl-ethanol hydrogensulfate gives under different conditions various products such as the ether (316) and the sulfone (317).288... 

Although numerous technical improvements in the production of carboxymethylcellulose are continually appearing in the patent literature,311 the basic reaction is essentially unchanged from that devised by Jansen1 and later improved by Chowdhury4 and Hoppler,6 in which cellulose (ROH) is steeped in caustic soda, and the alkali-cellulose is etherified by sodium monochloroacetate to form sodium carboxymethylcellulose plus sodium chloride. The reaction may be simply represented as follows. 

RSnBuj - ROH.1 This reaction can be effected by treatment of RSnBu3 with bromine, which effects cleavage of one butyl group to form an alkylbromodibutyl-stannane. This product is oxidized by basic m-chloroperbenzoic acid to an alcohol with retention of configuration. 

Thus, for this reaction, rAB will be independent of the concentration of alcohol. Therefore, while there should be a drastic change in concentration dependence, the activation energy should be changed only slightly because the basic displacement reaction of ROH(l) by ROH(2) is still the same. 

Only a catalytic amount of base is required as the deprotonation of ROH (which can be water or allyl alcohol) in the last step regenerates more alkoxide or hydroxide. It does not matter that sodium hydroxide (pICaH 15-7) is not basic enough to deprotonate an alcohol (pKa 16-17) completely, since only a small concentration of the reactive alkoxide is necessary for the reaction to proceed. 

ROH + (CH3CO) 20 -> CH3COOR + CH3COOH Amines undergo an analogous reaction to yield acetamides, the more basic amines having the greater activity ... 

Like water, alcohols and phenoljt are both weakly basic and weakly acidic, A weak batea, they are reversibly prutonoted by stronig acids to yield oxo nium ions, ROH ... 

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