FIGURE 2
"The
" E d u c t s " a n d " p r o d u c t s " of g r o u n d w a t e r c o n t a m i n a t i o n * "Educts"
"Products"
R—CH 2 —Br
R—CH2—S—CH2—R'
:CH —Br R'Br— C H 2 — C H 2 — C H 2 — C l Br—CH2—CH2—CH2—CH2—Br
P ^ C H — S—CH2—R"
Project SEED
R—CH2—S—CH2—CH2—CH2—Cl (CICH2CH2CH 2 ) 2 S
( R , R', R" = H, C H 3 , C2H5, C3H7, C4H9)
^ CH2
CH2 — C H 2 ^ CH2
s — s. . . and a suggested reaction s c h e m e
summer program gave me a chance to learn about research first hand."
R—CH2OH + B r (alcohol)
R—CH2—Br (bromide)
R — C H 2 — S — S - •CH 2 (dialkyldisulfide) '«£
£%
\S>s
(mercaptan)
R'—CH 2 Br R—CHaS" (mercaptanate)
SN2 k RS -
•
R—CH2—S—CH2—R' + (dialkylsulfide)
Br
Determined in the laboratory for R = R' = C5H11 kh = 1.96 χ 1CT7 s - 1 (pH = 8) »-1» (hydrolysis) = 40 d kHS- = 8.56 χ 10~" L m o l - 1 s - 1 k HS - = 8.06 χ 1 0 " 3 L m o r ' s " 1 PKHSH = 9.44
(T = 25
°C)
a
Contamination with halogenated hydrocarbons. For reactions involving primary alkyl bromides. Source: Presentation by René Schwarzenbach et al. of EAWAG, Diibendorf, Switzerland.
René Schwarzenbach and his colleagues at the Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG, Diibendorf, Switzerland) showed that certain brominated and bromochlorinated alkanes may undergo nucleophilic substitution reactions with hydrogen sulfide (H2S) to form organosulfur products. Schwarzenbach named the halogenated compounds introduced into the ground "educts" and noted that they had been discharged over a period of many years from an industrial plant that is now closed. In his laboratory experiments, Schwarzenbach used 1-bromohexane in water in the presence of H 2 S. Simulating "natural" underground anaerobic conditions of pH = 8 and [H2S]tot ~ 5 Χ ΙΟ"5 Μ, he was able to demonstrate the chemical formation of
sulfur-containing organics (Figure 2). Schwarzenbach pointed out that typ ical groundwater temperatures of 10 °C could cause such nucleophilic reactions and that at these lowered temperatures, "such nucleophilic re actions may well compete with hy drolysis," the more normal under ground water reaction of many alkyl halides. Other underground reactions of organic contaminants could include transformation or mineralization by microorganisms. These and other subsurface chemical and biochemical mechanisms are now beginning to come to light. Progress in this field is being made; nevertheless, much more work is needed to develop a sound sci entific basis for groundwater protec tion regulatory activity. —Julian Josephson
This summer, thanks to Project SEED, over 130 economically disadvantaged high school students like Angela Odom had a chance to work and learn in a number of academic research labs throughout the U.S. Your contributions, which are used 100% for student sti pends, are needed for SEED to continue helping students prepare for making vitally im portant decisions about their future education and work.
Project S E E D A C S , 1 1 5 5 16th St., N.W. W a s h i n g t o n , D.C. 2 0 0 3 6 Y e s , I'd like to h e l p t h e s e s t u d e n t s learn w h a t is r e q u i r e d for s u c c e s s as college students.
Name:
„
Address:
Contribution: Π $50
Π $20
Π
$10
Π Other
Environ. Sci. Technol., Vol. 17, No. 11, 1983
521A
