10-06-02 14:31
No 365034
1-Chlorobutane — A Useful Solvent for Recrystallizations
Aldrichimica Acta, 34(2), p34 (2001)
When carrying out a recrystallization, there are sometimes problems with the choice of solvent and recourse is made to mixed solvents. Of these, the combination ethyl acetate–petroleum ether is perhaps the most common pairing. Usually, one obtains a hot solution by addition of the more polar solvent to a hot suspension of the would-be solute in the less polar solvent. However, on cooling there is frequently development of two phases followed by precipitation of the solute as a solid mass rather than as crystals of good texture. After some experiences as outlined above, we sought an alternative approach. What we were seeking was a solvent of low but definite polarity, with a convenient boiling point. We chose 1-chlorobutane, bp 77–78°C, and we have found this to be a convenient solvent for the recrystallization of oxime ethers [1]; nitrogen ylides, such as Me3N+–N––CN (with no butylation of the ylide) [2]; and 3-pyrrolylpentanoic acid [3]. In unpublished work, we have used 1-chlorobutane to advantage in the recrystallization of the nitrogen ylide Me3N+–N––C(=O)Me (again without butylation), and the bicyclic compounds 1-nitrocamphene and camphor-4-carboxylic acid. Although the bulk dielectric constant does not tell the whole story about a solvent, 1-chlorobutane, interestingly, has a higher dielectric constant (7.28) than ethyl acetate (6.08); that of n-hexane is 1.89. [4] Specific solute–solvent interactions also need to be taken into account.
We recommend that 1-chlorobutane be considered as a solvent for recrystallization in appropriate cases subject to a couple of caveats: (a) manipulations with the solvent be carried out in a fume cupboard, and (b) one is mindful that 1-chlorobutane may be attacked by nucleophiles, though its reactivity is, at best, sluggish. For recrystallizations that require a higher temperature, 1-chloropentane is worth consideration.
References:
(1) Bradley, G.W.; Morris, D. G. J. Chem. Res. (S) 1993, 220.
(2) Chardin, A.; Berthelot, M.; Laurence, C.; Morris, D. G. J. Phys. Org. Chem. 1995, 8, 626.
(3) Ryder, K. S.; Morris, D. G.; Cooper, J. M. Langmuir 1996, 12, 5681.
(4) CRC Handbook of Chemistry and Physics, 79th ed.; Lide, D. R., Ed.; CRC Press LLC: Boca Raton, FL, 1998–1999; Section 6, pp 139–161.
(Hive Bee)
10-06-02 14:33
No 365035
...
[pH]armacist - Never underestimate the power of retrosynthesis. Svenskar suger på fotboll!
(Hive Bee)
10-06-02 15:38
No 365045
1-BuCl is sometimes used for the extraction of amphetamines from urine as well.
WOMAN.ZIP: Great Shareware, but be careful of viruses...
(Stranger)
10-06-02 21:10
No 365089
On the topic of crystallization, not neccessarily recrystallization per se, I have found that preparing a 6N sol. of aq.HCl and mixing this 1:1 with crushed ice, and adding an appropriate amount of a freebase, set to stir until "slushie-like" and pouring into a buchner for vacuum filtration provides a quick and easy alternative to titration/evaporation or gassing/filtration.
Pr(+)tium
(Chief Bee)
10-06-02 21:48
No 365097
That surely must depend completely on what you are trying to crystallize. Many amine hydrochlorides are too soluble even in cold water to allow for that.
(Hive Bee)
10-07-02 12:02
No 365424
Which amine hydrochlorides falls out of solution under those conditions? To me it seems very strange considering the HUGE amounts of water, regardless of the low temperature.
Catalytic hydrogenation freak