301
Photoinduced and Microbial Degradation
P-atom-containing functional groups bonded to a given compound in the aqueous phase forming a 2σ/1σ * two-center-three-electron (2c–3e) adduct (Bonifac ˇic ˇ
1999). These functional groups also affect the H-atom abstraction reaction by
donating or withdrawing electrons on the C–H bonds. The group rate constant,
k R4 (Eq. 2.13) represents the reaction of HO
• with S-, N-, or P-atom-containing
compounds. The influence of neighboring functional groups is considered as negligible. The rate constant, k, for HO
• addition to iminodiacetic acid (HOOC–CH 2 –
NH–CH 2 –COOH) as a typical example is expressed below (Eq. 2.23):
It is shown that the group rate constants k –CN and k –NH2 can be compared with
the rate constants for compounds that react with HO
• via only interaction such
as cyanogen and thiourea, respectively. The rate constant for thiourea (which
has two –NH 2 groups) is approximately twice k –NH2 , because the electron positive –CS– functional group does not significantly affect the electron density of
the N atom. The reaction of HO
• with urea is presumably different because the
two amine functional groups of urea are bonded to the electron-negative functional group, –CO–. Thus, another group rate constant k –N–CO–N– is considered
for methylurea, tetramethyl urea, and 1,3-dimethylurea. The magnitude of most
group rate constants for the S-containing compounds is of the same order as for
the amine-containing ones, but approximately 1 order of magnitude larger than
for the amide-containing compounds. This might be caused by the electronegative –CO– functional group of the amide. The S-, N-, or P-atom-containing
group contribution factors apparently play the same role as the functional groups
for H-atom abstraction, i.e., X Ri = e −(Ea, absRi)/RT . However, it is anticipated
that S-, N-, or P-atom-containing functional groups may have different effects
on H-atom abstraction. The group contribution factors for –S, –S–S–, and –SH,
and –NH 2 , –NH–, and –N<, respectively, are assumed to be identical due to the
following reasons: (1) limited data availability for single functional group compounds, (2) similar electron inductive ability, and (3) application for the gaseous
phase. In addition, the same data sets for the S– and N-atom-containing compounds are used to calibrate the group rate constants, k –S– , k –S–S– , and k –SH , and
k –NH2 , k –NH– , and k –N< , respectively. These group rate constants are not assumed
to be identical because the interaction of HO
• with each functional group might
be more significant than the electron donating effects of the functional groups.
For similar electron inductive ability, the Taft constant indicates similar values among the S– and N-atom-containing functional groups. For example, the
Taft constants for SCH 3 , SC 2 H 5 , and SH are 1.66, 1.44, and 1.52, respectively
(Karelson 2000), and those for NH 2 , NHCH 3 , N(CH 3 ) 2 , NH(CH 2 ) 3 CH 3 , and
N(C 2 H 5 ) 2 are 0.62, 0.94, 1.02, 1.08, and 1.00, respectively (Karelson 2000).
These values are well distinguished from 3.61 of NH 3
+ , 4.66 of NO 2 , 4.16 of
N + (CH 3 ) 3 , and 3.64 of CN. Finally, it is assumed that the group contributed factors for –S–,–S–S–, and –SH, and for –NH 2 , –NH–, –N< , –NNO, and –NNO 2
are identical, which successfully predicted the gas-phase HO
• rate constants
(Atkinson 1986, 1987; Kwok and Atkinson 1995). A linear correlation between
(2.23)
k = 2 × 2k
o
sec X −COOH X −NH− + k −NH− + 2k −COOH
Photoinduced and Microbial Degradation
P-atom-containing functional groups bonded to a given compound in the aqueous phase forming a 2σ/1σ * two-center-three-electron (2c–3e) adduct (Bonifac ˇic ˇ
1999). These functional groups also affect the H-atom abstraction reaction by
donating or withdrawing electrons on the C–H bonds. The group rate constant,
k R4 (Eq. 2.13) represents the reaction of HO
• with S-, N-, or P-atom-containing
compounds. The influence of neighboring functional groups is considered as negligible. The rate constant, k, for HO
• addition to iminodiacetic acid (HOOC–CH 2 –
NH–CH 2 –COOH) as a typical example is expressed below (Eq. 2.23):
It is shown that the group rate constants k –CN and k –NH2 can be compared with
the rate constants for compounds that react with HO
• via only interaction such
as cyanogen and thiourea, respectively. The rate constant for thiourea (which
has two –NH 2 groups) is approximately twice k –NH2 , because the electron positive –CS– functional group does not significantly affect the electron density of
the N atom. The reaction of HO
• with urea is presumably different because the
two amine functional groups of urea are bonded to the electron-negative functional group, –CO–. Thus, another group rate constant k –N–CO–N– is considered
for methylurea, tetramethyl urea, and 1,3-dimethylurea. The magnitude of most
group rate constants for the S-containing compounds is of the same order as for
the amine-containing ones, but approximately 1 order of magnitude larger than
for the amide-containing compounds. This might be caused by the electronegative –CO– functional group of the amide. The S-, N-, or P-atom-containing
group contribution factors apparently play the same role as the functional groups
for H-atom abstraction, i.e., X Ri = e −(Ea, absRi)/RT . However, it is anticipated
that S-, N-, or P-atom-containing functional groups may have different effects
on H-atom abstraction. The group contribution factors for –S, –S–S–, and –SH,
and –NH 2 , –NH–, and –N<, respectively, are assumed to be identical due to the
following reasons: (1) limited data availability for single functional group compounds, (2) similar electron inductive ability, and (3) application for the gaseous
phase. In addition, the same data sets for the S– and N-atom-containing compounds are used to calibrate the group rate constants, k –S– , k –S–S– , and k –SH , and
k –NH2 , k –NH– , and k –N< , respectively. These group rate constants are not assumed
to be identical because the interaction of HO
• with each functional group might
be more significant than the electron donating effects of the functional groups.
For similar electron inductive ability, the Taft constant indicates similar values among the S– and N-atom-containing functional groups. For example, the
Taft constants for SCH 3 , SC 2 H 5 , and SH are 1.66, 1.44, and 1.52, respectively
(Karelson 2000), and those for NH 2 , NHCH 3 , N(CH 3 ) 2 , NH(CH 2 ) 3 CH 3 , and
N(C 2 H 5 ) 2 are 0.62, 0.94, 1.02, 1.08, and 1.00, respectively (Karelson 2000).
These values are well distinguished from 3.61 of NH 3
+ , 4.66 of NO 2 , 4.16 of
N + (CH 3 ) 3 , and 3.64 of CN. Finally, it is assumed that the group contributed factors for –S–,–S–S–, and –SH, and for –NH 2 , –NH–, –N< , –NNO, and –NNO 2
are identical, which successfully predicted the gas-phase HO
• rate constants
(Atkinson 1986, 1987; Kwok and Atkinson 1995). A linear correlation between
(2.23)
k = 2 × 2k
o
sec X −COOH X −NH− + k −NH− + 2k −COOH