Propanoates

Isobutyl alcohol, isobutanol, 2-methyl-propanol, isopropyl carbinol, Me2CHCH20H. B.p. 108°C. Occurs in fusel-oil. Oxidized by potassium permanganate to 2-methyl-propanoic acid dehydrated by strong sulphuric acid to 2-methylpropene. 

If triphenylmethyl chloride in ether is treated with sodium, a yellow colour is produced due to the presence of the anionic spiecies PhsC". Alternatively, if triphenylmethyl chloride is treated with silver perchlorate in a solvent such as THF, the triphenylmethyl cation is obtained. More conveniently, triphenylmethyl salts, PhsC X", can be obtained as orange-red crystalline solids from the action of the appropriate strong acid on triphenylcarbinol in ethanoic or propanoic anhydride solution. The perchlorate, fluoroborate and hexafluoro-phosphate salts are most commonly used for hydride ion abstraction from organic compounds (e.g. cycloheptatriene gives tropylium salts). The salts are rather easily hydrolysed to triphenylcarbinol. 

A solution of 2-aminobenzophenone (98 g, 0.50 mol) and methyl 2-(methyl-thio)propanoate (74 g, 0,50 mol) in CH Clj (21) was cooled to —70 C and 95% 7-butyl hypochlorite (56 g, 0.5 mol) was added dropwise at such a rate that the temperature did not rise above — 65 C. One hour after the addition was complete, EtjN was added and the mixture was allowed to come to room temperature. The solution w as mixed with 3 N HCl (800 ml) and stirred for 1 h. The organic layer was separated, dried (Na2S04 ) and filtered. The solution was evaporated in vacuo and the residue triturated with ether. Filtration gave the 3-(methylthio)oxindole intermediate (92 g) in 62% yield. 

In situ quaternization method ethyl 2-(ethoxycarbonyl)-2-formamido-3-(indol-3-yl)propanoate[7,8J... 

Ethyl 2-nitro-3-(5-benzyloxyindoT3-yl)propanoate (3.7 g, 0.01 mol) was dissolved in abs. ethanol (50 ml) and hydrogenated over PtO catalyst (EOg) until H2 uptake ceased (about 1.75 h). The solution was purged with nitrogen and 20% aq. NaOH solution (4.0 g) w as added. A hydrogen atmosphere was re-established and the hydrolysis was allowed to proceed overnight. The solution was diluted with water (20 ml) and filtered. The pH of the filtrate was adjusted to 6 with HOAc and heated to provide a solid precipitate. The mixture was cooled and filtered to provide 5-benzyloxytryptophan (2.64 g). 

A solution of benzyl 5-methoxyindole-3-propanoate (26Og, 0.084mol) in... 

The barriers to rotation about the N-C bond have been determined b dynamic nuclear magnetic resonance for A -isopropyl (80. 81). propanoic acid (74). A -ethyl (82). N-benzyl. and A -neopentyl substituents (82). Selected values of these barriers are given in Tables VII-6 and VII-7. 

As actually carried out in the laboratory 3 moles of propanoic acid was used per jnole of 1 butanol and the desired ester was obtained in 78% yield ... 

Carboxylic acids are fairly polar and simple ones such as acetic acid propanoic acid and benzoic acid have dipole moments m the range 1 7-1 9 D... 

Convincing evidence that ester hydrolysis in base proceeds by the second of these two paths namely nucleophilic acyl substitution has been obtained from several sources In one experiment ethyl propanoate labeled with 0 m the ethoxy group was hydrolyzed On isolating the products all the 0 was found m the ethyl alcohol there was no 0 enrichment m the sodium propanoate... 

NMR Chemical shift differences m their H NMR spectra aid the structure deter mmation of esters Consider the two isomeric esters ethyl acetate and methyl propanoate As Figure 20 9 shows the number of signals and their multiplicities are the same for both esters Both have a methyl singlet and a triplet-quartet pattern for their ethyl group... 

FIGURE 20 9 The 200 MHz H NMR spectra (a) ethyl acetate and (b) methyl propanoate... 

The saponification of 0 labeled ethyl propanoate was desenbed in Section 20 11 as one of the significant expenments that demonstrated acyl-oxygen cleavage in ester hydrolysis The 0 labeled ethyl propanoate used in this expenment was prepared from 0 labeled ethyl alcohol which in turn was obtained from acetaldehyde and 0 enriched water Wnte a senes of equations... 

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