edited by
Ralph K. Birdwhistell
textbook forum The Water Solubility of 2-Butanol: A Widespread Error Donald B. Alger
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California State University Chico, CA 95929
While using a currently popular organic chemistry text as a source of data for comparing relative solubilities of some alcohols and ketones, it was observed that the solubility of 2-butanol which was given as 12.5 g per 100 g of water was much lower than expected. In general, secondary alcohols have approximately the same solubility as the corresponding ketones and the solubility of 2-butanone is about 26 g per 100 g of water. It was found that of 12 recentedition organic texts five gave quantitative solubility data for 2-butanol and they all had this same value. In addition, the older editions of the CRC Handbook of Chemistry and Physics, which still listed quantitative solubilities, and Lange’s Handbook of Chemisty also gave this value. The Merck Index lists an even lower solubility of one part in 12 parts of water (approximately 8 g per 100 g of water). However, solubility values of 26.0, 22.5, and 18.0 g per 100 g of solution at 20,25, and 30 °C, respectively, were reported by Alexejew in 1886, with similar results reported by Dolgolenko in 1907 and Dryer in 1913. This information was compiled and cited in 1941 by Seidell,1 Current industrial data provided in a compilation of material safety data sheets,2 indicate a solubility of 20.00 lb per 100 lb of water at 68.0 °F. This is equivalent to 20 g per 100 g of water at 20 °C. The origin of this error is undoubtedly from Beilstein’s Handbuch der Organischen Chemie. The main work (das Hauptwerk), which covers the literature through 1909, cites a solubility reported by Norris and Green3 of one part alcohol per eight parts of water. This corresponds to 12.5 g per 100 g of water. Interestingly no other citations regarding the solubility of 2-butanol appear there or in any subsequent supplement of Beilstein. As minor as this error might seem, it is worth bringing it to the attention of the readers of this Journal, because it is so widespread and errors of this type can make it appear that there exists a serious lack of predictability in chemistry for as simple a property as solubility. This frustrastes both students and instructors. In addition, this provides a good example of the potential risk of using data from secondary sources without verifying the information in the primary literature. Seidell, A. Solubilities of Organic Compounds, 3rd ed.; D. Van Nostrand: New York, 1941; Vol. 2, p. 269. 2U.S. Department of Transportation; the U.S. Coast Guard Chemical Hazard Response Information System (CHRIS); Superintendent of Documents, U.S. Government Printing Office: Washington, DC. 3Norri$, J. F.; Green, E. H. American Chemical Journal 1901, 26, 305. 1
Universtiy of West Florida Pensacola, FL 32504
Intensity and Rate of a Photochemical Reaction John M. Simmie University College Galway, Ireland
For
a
chemical reaction such aA
bB
+
+
pP
=
...
as +
gQ
+
...
the rate of reaction per unit volume (v, R, defined 1 _
d[A]
_
"_
a
dt
1
d[PJ
p
dt
= "
"
or Qi)
is normally
“_
"
mol-m-3
s_1
(1)
This is only true for systems at constant volume. A more universal definition is given by the rate of conversion dq
^
1
d rij
vi ^
mol s-1 (2)
where £ is the extent or advancement of reaction, vf is the stoichiometric coefficient, and n, is the chemical amount of species i. The difference between these definitions (eqs 1 and 2) is partly responsible for the confusion that exists about the correct way to describe photochemical reactions. For example, for a photochemical reaction Br2 + hv
—»
Br
+
Br
(3)
the rate of reaction is quoted in various ways:
“If
or
the number of photons absorbed per unit time and unit
volume (J).
“
