N-Pentyl bromide

The second-order rate constants for the reaction of thiosulfate ion with n-pentyl bromide (equation 38) in aqueous ethanol (25/74 and 44/56, w/w) were affected similarly by cationic and anionic surfactants. CTAB increased the second-order rate constant by a factor of ca. 9-5 and NaLS decreased it slightly, but not unexpectedly, a non-ionic surfactant, polyoxyethylene(24) dinonylphenol did not significantly alter the rate constant (Bunton and Robinson, 1968). 

Aliphatic and aromatic nucleophilic substitution reactions are also subject to micellar effects, with results consistent with those in other reactions. In the reaction of alkyl halides with CN and S Oj in aqueous media, sodium dodecyl sulfate micelles decreased the second-order rate constants and dodecyltrimethylammonium bromide increased them (Winters, 1965 Bunton, 1968). The reactivity of methyl bromide in the cationic micellar phase was 30 to 50 times that in the bulk phase and was negligible in the anionic micellar phase a nonionic surfactant did not significantly affect the rate constant for n-pentyl bromide with S2O3-. Micellar effects on nucleophilic aromatic substitution reactions follow similar patterns. The reaction of 2, 4-dinitrochlorobenzene or 2, 4-dinitrofluorobenzene with hydroxide ion in aqueous media is catalyzed by cationic surfactants and retarded by sodium dodecyl sulfate (Bunton, 1968, 1969). Cetyltrimethylammonium bromide micelles increased the reactivity of dinitrofluorobenzene 59 times, whereas sodium dodecyl sulfate decreased it by a factor of 2.5 for dinitrochlorobenzene, the figures are 82 and 13 times, respectively. A POE nonionic surfactant had no effect. 

Didiloromethyl ketones. n-Pentylmagnesium bromide prepared from n-pentyl bromide refluxed 2 hrs. with (tridilorovinyl)diethylamine in ether, treated 0.5 hr. with 10%-H2S04 at 0°, and refluxed 3 hrs. -> l,l-didiloro-2-heptanone. Y 77%. F. e., also isolation of the intermediate enamines, s. J. Ficini and A. Dureault, Bl. 1974, 1533 s. a. C. Wiaux-Zamar et al., Ang. Ch. 88, 417 (1976). 

Preparation by reaction of n-pentyl bromide with 5-allyl-2,4-dihydroxyacetophenone in the presence of potassium carbonate and potassium iodide in refluxing methyl ethyl ketone (43-44%) [2671,2678,2679]. 

Table L Pseudo First Order Rate Constants (90 C) for the Cyanation of n-Pentyl Bromide in the Presence of a Hectorite-Supported Triphase Catalyst and...

Neopentyl (2,2-dimethylpropyl) systems are resistant to nucleo diilic substitution reactions. They are primary and do not form caibocation intermediates, but the /-butyl substituent efiTectively hinders back-side attack. The rate of reaction of neopent>i bromide with iodide ion is 470 times slower than that of n-butyl bromide. Usually, tiie ner rentyl system reacts with rearrangement to the /-pentyl system, aldiough use of good nucleophiles in polar aprotic solvents permits direct displacement to occur. Entry 2 shows that such a reaction with azide ion as the nucleophile proceeds with complete inversion of configuration. The primary beiuyl system in entry 3 exhibits high, but not complete, inversiotL This is attributed to racemization of the reactant by ionization and internal return. 

Chemical Name n-amyl bromide, 1-bromopentane, monobromopentane, pentyl bromide... 

Maccoll et have pointed out that along the series of primary bromides (n-propyl, n-butyl, n-pentyl, n-hexyl) the chain component of the overall thermal decomposition undergoes a steady decrease relative to the unimolecular component of the decomposition. This has been attributed to the increased probability of formation of -radicals with increase in the length of the carbon chain in the molecule. The decomposition of secondary monobromides is mainly unimolecular with only a slight radical-chain component. Tertiary monobromides decompose uni-molecularly. 

Some years later, stereoselective syntheses of a variety of optically active esters of arsinthious acids were reported. The esters were prepared by treating secondary chloroarsines with thiols in the presence of (—)-N,N-diethyl-a-methylbenzylamine. The n-pentyl ester 135, when allowed to react with n-propylmagnesium bromide, gave (R)-(—)-65 with low stereoselectivity and inversion at arsenic as indicated in equation 19 (Table... 

Figure 2 Four representative Grignard reagents plotted according to Eq. (5) cyclohexyl bromide vs. cyclopentyl bromide ( ) cyclopentyl chloride vs. cyclopentyl bromide (A) n-pentyl chloride vs. cyclohexyl chloride ( ) neopentyl bromide vs. cyclopentyl bromide (O)- (From Ref. 81b.)...

Kennedy et al. used living cationic polymerization from a tricumyl initiator to prepare an allyl-terminated 3-arm star of pIB, followed by hydroboration/oxida-tion to generate hydroxy chain ends which were esterified with 2-bromoisobutyryl bromide to generate the ATRP trifunctional macroinitiator (Scheme 58) [354]. They subsequently carried out ATRP of MMA in toluene using the Cu(I)/N-( -pentyl)2-pyridylmethanimine catalyst system with the addition of Cu° powder [242] to maintain a sufficient concentration of active Cu(I) [354]. Macroinitiators of Mn=9200 and 15,000 were prepared and both had narrow molecular weight distributions (Mw/Mn=1.15 and 1.09, respectively). The formation of block copoly-... 

A further comparison is possible between n-pentyl and vinyl bromides, viz. 

A number of examples of dealkylations by chemical and catalytic methods are given in Table 4.7 (refs.89-93). A very general method for the cleavage of phenolic ethers consists in their reaction under reflux during 36 hours with an excess of 37% hydrobromic acid and a small amount of hexadecylammonium bromide. Phenyl n-pentyl ether gave phenol in 71% yield (ref.94). 

Bromine added slowly to a cooled soln. of triphenylphosphine in benzonitrile, heated to 125°, n-pentyl ether added, and the product isolated after ca. 4 hrs. -> 77-pentyl bromide. Y 77.8%. — This ether cleavage avoids the strongly acidic conditions commonly, or the strongly basic conditions sometimes employed. F. e. s. A. G. Anderson, Jr., and F. J. Freenor, Am. Soc. 86, 5037 (1964). 

These reactions provide an interesting contrast in mechanisms. The n-butyl bromide synthesis proceeds by an Sj 2 mechanism, whereas f-pentyl chloride is prepared by an S l reaction. 

EXPERIMENT 23 Synthesis of n-Butyl Bromide and t-Pentyl Chloride 201... 

As your instructor indicates, perform either the n-butyl bromide or the f-pentyl chloride procedure or both. 

A mixture of 3-methyl-pentyl bromide, mer-captosuccinic acid, 1.33 N KOH, n-propanol, and some boiling chips refluxed several hrs. 

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