Why does a color-developing phenomenon occur on thermal paper comprising of a fluoran dye and a color developer molecule?

Article abstract of DOI:10.1246/bcsj.75.2225

The mechanism of the color development on thermal paper, comprising a fluoran dye (S-205) and a color developer molecule, such as bisphenol A, was elucidated based on spectroscopic analyses (IR, and NMR) on an isolated black-colored compound prepared by a reaction of S-205 and bisphenol A. We propose that this black-colored compound is, indeed, a color-developing complex (CDC) with a definite molar ratio (S-205:bisphenol A = 1:4) which has been formed between the open-form S-205 (generated by the cleavage of the lactone ring of S-205: zwitterion) and bisphenol A through hydrogen-bonding. The enthalpy gain associated with the formation of CDC plays an important role for black-color formation on thermal paper.

Full text of DOI:10.1246/bcsj.75.2225

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 2225–2231 (2002) 2225
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Why Does a Color-Developing Phenomenon Occur on Thermal Paper
Comprising of a Fluoran Dye and a Color Developer Molecule?
Color Developing Phenomenon on Thermal Paper
Y. Takahashi et al.
Yoshiyuki Takahashi, Ayako Shirai, Takako Segawa,† Tatsuya Takahashi,† and Kazuhisa Sakakibara*,†
02
25
31
SJA8
09-2673
121
Advanced Technology Research Laboratory, Oji Paper Company, 1-10-6 Shinonome, Kohtoh-ku, Tokyo 135-8558
†Department of Applied Chemistry, Yokohama National University,
79-5 Tokoiwadai, Hodogaya-ku, Yokohama 240-8501
(Received May 10, 2002)
02
02
.4
The mechanism of the color development on thermal paper, comprising a fluoran dye (S-205) and a color developer
molecule, such as bisphenol A, was elucidated based on spectroscopic analyses (IR, and NMR) on an isolated black-col-
ored compound prepared by a reaction of S-205 and bisphenol A. We propose that this black-colored compound is, in-
deed, a color-developing complex (CDC) with a definite molar ratio (S-205:bisphenol A = 1:4 ) which has been formed
between the open-form S-205 (generated by the cleavage of the lactone ring of S-205: zwitterion) and bisphenol A
through hydrogen-bonding. The enthalpy gain associated with the formation of CDC plays an important role for black-
color formation on thermal paper.
Thermal paper is presently widely used in our daily life be-
cause of the easiness of printing that requires simple hardware
for quick printing, which can make printing devices compact
and practically maintenance-free. Thermal paper1 is composed
of a supporting material (paper) and a coating layer in which a
fluoran dye precursor, a color developer, and a sensitizer are
dispersed uniformly as fine particles. When a certain surface
area on thermal paper is heated by the thermal head of the
printer, the fluoran dye precursor, the color developer, and the
sensitizer melt together and form a color as the result of a
chemical reaction. Among many fluoran dyes, 2ꢀ-anilino-6ꢀ-
(N-ethyl-N-isopentyl) amino)- 3ꢀ- methylspiro[isobenzofuran-
1(3H), 9ꢀ-(9H)xanthen]-3-one, hereafter referred to as S-205,
is widely used as a dye precursor for black color development;
the black color is due to the strong absorption maxima of this
dye in the visible region at around 450 (yellow) and 590 nm
(purple), which are in a relation of complementary colors.
A simple acid-base equilibrium mechanism2 for color devel-
oping has been proposed and accepted without any definite ex-
perimental evidence until now. That is, a proton released from
phenols attacks an ester oxygen atom in the fluoran dye (S-
205, for example), which leads to a cleavage of the lactone-
ring, as shown in Scheme 1. By opening the lactone ring, the
electronic state of spiro-carbon in S-205 changes from sp3 hy-
bridization to sp2, and π-electron conjugation in the xanthene
ring extends over to give rise to a black-color formation. Al-
though it is experimentally sure that black-color development
of the dye occurs by the addition of strong acids, such as HCl
and CH3COOH, a question prevails as to whether the same
mechanism works between dyes and phenols, because; (1) the
acidity of phenols is known to be weak (pKa is 8–11)3, (2) car-
boxy functional group generated in the dye as a result of the
cleavage of the lactone-ring takes the carboxylate form
(–COO−), not the carboxylic acid form (–COOH), which was
elucidated from IR spectrum measurements (see Results and
Discussion), and (3) the above color-developing reaction pro-
ceeds more in solvents with less polarity than in high polarity.
We, in this paper, propose an alternate, or co-working, mecha-
nism for color developing phenomena on thermal paper, be-
tween a fluoran dye and phenols, represented here by bisphe-
nol A.
The new mechanism is based on our findings that a black-
colored compound between S-205 and bisphenol A can be iso-
lated under certain experimental conditions. This compound
was characterized to be a molecular complex (Color Develop-
ing Complex, CDC) consisting a definite molecular ratio of
the dye and the color developer. We deduce that CDC is stabi-
lized by the hydrogen bonding interaction between the dye and
the color developer.
Results and Discussion
Preparation and Isolation of the Color Developing Com-
plex (CDC). The color developing complex (CDC) was pre-
pared as black precipitates by dissolving both S-205 and color
developer bisphenol A in hot toluene, and rapidly cooling
down the toluene solution in an ice bath. Slow cooling-down
and prolonged cooling precipitated solely bisphenol A crystals
and obscured the molar ratio of the two components in the pre-
pared CDC. The obtained black precipitates were quickly fil-
tered and washed by cold toluene with suction, and then dried
in vacuo to give rise to a black powder. This black powder is
fairly stable as long as it is in the solid state. However, its
black color disappears soon when it contacts with oil and vari-
ous organic solvents.
Infrared (IR) Spectrum of CDC. The frequencies of the
characteristic CwO stretching vibration peaks of the CDC and
relevant compounds are summarized in Table 1, and their IR
spectra are shown in Fig. 1. The IR spectrum of the CDC indi-

2226 Bull. Chem. Soc. Jpn., 75, No. 10 (2002)
Color Developing Phenomenon on Thermal Paper
Scheme 1.
Table 1. Infrared Spectra in the Region of the CwO Stretching Vibrations of S-205 + Bisphe-
nol A Coler Developing Complex: CDC and Its Relevant Molecules
Compound
Wavenumber / cm−1
Measurement
condition
(S-205+Bisphenol A) CDC
1639 (anti-symmetric)
1362 (symmetric)
KBr disc
S-205
1751
1759
KBr disc
in CCl4
Lactone ring opened S-205
cates that the proposed acid-base equilibrium mechanism for
color developing (Scheme 1) can not be justified. An IR spec-
trum of the lactone form S-205 in KBr disc showed a charac-
teristic CwO stretching vibration inherent to a lactone func-
tional group at 1751 cm−1. However, carbonyl vibration of the
black-colored CDC appeared at 1639 cm−1. This wavenumber
is rather low to be assigned as a CwO stretching vibration
mode in the –COOH group. The standard IR spectrum data
book4 has reported that the CwO vibration of aromatic carbox-
peared at 1759 cm−1, which can be assigned to the COOH
group. Though both compounds (CDC and open-form S-205
in the strong acid) showed a black color, the IR spectra of these
compounds indicate that they exist as different chemical spe-
cies; i.e. the CDC exists as a zwitterion, and the open-form S-
205 generated by the reaction with strong acids exists as a lac-
tone ring-opened carboxylic acid, as shown in Scheme 1,
which is in good agreement with a previous report by Nakat-
su’s group.5 The principal factor to stabilize the CDC can be
attributed to hydrogen bonding between S-205 and bisphenol
A. The hydroxy group in bisphenol A works as a hydrogen-
bond donor to form a hydrogen bond with electron-rich hydro-
gen-bond acceptor atoms in the zwitterionic form of S-205.
Chemical Properties of the CDC. This isolated black-
colored CDC is a thermodynamically metastable compound.
For instance, it gradually degrades to the starting materials (S-
205) and color developer bisphenol A when heated, particular-
ly under high humidity (i.e. black-color compound turns to
colorless one). The degradation was confirmed by detecting
the formation of bisphenol A crystals from the CDC after the
treatment. In addition, CDCs are found to be dissolved in
many hydrogen-bond forming solvents, such as alcohols, di-
methyl sulfoxide, and acetone, to give a colorless solution,
which indicates the complete dissociation of the CDC to the
ylic acids (Ar–COOH) appears at around 1680–1700 cm−1
,
while characteristic vibration modes inherent to carboxylate
–COO− appear at 1610–1550 cm−1 (anti-symmetric mode car-
bonyl vibration of COO−) and 1420–1300 cm−1 (symmetric
mode of COO−). The IR spectrum of the CDC also showed a
symmetric mode carbonyl vibration at 1362 cm−1. A lower
wavenumber shift (100 cm−1) and the emergence of symmetric
mode –COO− vibration of the CDC indicate the existence of a
carboxylate functional group (–COO−) in the CDC instead of
a carboxyl group (–COOH). In order to make sure that S-205
in the CDC really exists a zwitterion, the IR spectrum of the
open-form S-205, as shown in Scheme 1 (which can be gener-
ated by the reaction with HCl to lead the cleavage of the lac-
tone ring) was measured in CCl4. In the IR spectrum of this
open-form S-205, a carbonyl CwO stretching vibration ap-

Y. Takahashi et al.
Bull. Chem. Soc. Jpn., 75, No. 10 (2002) 2227
Fig. 2. Molar ratio of CDC (S-205:bisphenol A) determined
1H-NMR measurements by changing the composition of
the starting mixture (S-205:bisphenol A = 1:1 – 1:6).
vents, it was found that this phenomenon takes time in such
solvents as CDCl3, a solvent with a certain polarity to dissolve
the CDC, yet having a less hydrogen bond-forming nature.
By taking advantage of this slow process of dissociation, we
could obtain some structural information of CDC from the
13C-NMR spectrum immediately after preparing a sample so-
lution by comparing with that of the ring-closed (lactone) form
of S-205. The 13C-NMR spectrum data of the lactone form S-
205 are summarized in Table 2.
We found that a peak corresponding to the spirocarbon (C9),
which would drastically change its atom configuration during
the course of color development, showed both broadening and
a considerable decrease in the intensity of CDC. Similar phe-
nomena were observed for the C5, C6, C7 and C8 atoms, that
were thought to bear a partial charge appearing on the spiro-
carbon in the colored form. Peak broadening and a reduction
of the intensity in smaller magnitude were also observed for
the alkylamino carbons at the C6 position. It should be noted
here that other carbons did not experience these peak changes,
even immediately after sample preparation. Both the broaden-
ing and peak reduction phenomena disappeared after several
hours to give identical peaks to the lactone form of S-205 (and
bisphenol A). The broadening of the 13C-NMR peaks and the
decrease in the signal intensity on some specified carbon atoms
in S-205 can be attributed to an inter-molecular interaction be-
tween S-205 and bisphenol A. The inter-molecular interaction
may restrict the molecular motion at the interactive-sites. As a
result of the restriction of molecular motion at specific carbon
atoms, the effective correlation times at these carbon atoms
(τc) would be longer. Because the signal line-width (∆ν1/2), re-
laxation time (T1), and effective correlation time (τc) are corre-
lated with each other, as shown in Eq. 1,7 we can recognize a
restriction of molecular motion (i.e. the longer effective corre-
lation time) would lead to a broadening of the peak and a de-
crease of the signal intensities,
Fig. 1. IR spectra of the S-205 + bisphenol A Color Devel-
oping Complex (CDC) and its relevant molecules.
consisting dye and phenols. Due to this metastablity of the
CDC, experiments in the liquid phase do not lead to the inher-
ent character of the CDC. However, both HPLC analyses (col-
umn; LiChrospher 100RP18e, eluate; CH3CN:H2O:phosphor-
ic acid) and 1H-NMR measurements of the CDC solution have
determined that the molar ratio of the CDC has a constant val-
ue of S-205:bisphenol A = 1:4, regardless of the composition
of the starting materials in hot toluene (S205:bisphenol A was
altered from 1:1 to 1:6), as shown in Fig. 2. This result
strongly suggests that S-205 and color developer bisphenol A
interact to form a well-fixed complex as a black solid.6
2
2
∆ν1/2 ꢁ 1 / T1 = h2γC γH rCH−6Nτc ,
(1)
where γC and γH are the gyromagnetic ratios of the carbon and
hydrogen atoms, respectively. rCH is the interatomic distance
between the C and H atoms. N is the number of directly adja-
13C-NMR Spectra of S-205 and the CDC. Although the
CDC dissociates into its component molecules in organic sol-

2228 Bull. Chem. Soc. Jpn., 75, No. 10 (2002)
Color Developing Phenomenon on Thermal Paper
Table 2. The 13C-NMR Spectral Peaks’Assignment of S-205 Measured in CDCl3
Chemical shift / ppm
Assignment
Chemical shift / ppm
Assignment
12.10
17.88
22.46
25.68
35.60
44.30
47.95
84.43
96.80
103.97
108.35
114.67
116.85
118.37
118.58
C25
C23
C29, C30
C28
C27
C24
C26
C9
C5
C8a
C7
C22, C18
C9a
119.48
123.88
124.38
126.09
128.80
128.97
129.90
134.82
136.75
145.12
146.41
149.27
152.34
152.38
168.73
C1
C11
C14
C10
C8
C19, C21
C13
C5a
C4a
C3
C15
C6
C17
C2
C4
C20
C16
cent protons.
This interesting behavior of the 13C-NMR spectrum in an in-
ert solvent, such as CDCl3, was not observed in polar protic
and aprotic solvents. In the case where a noticeable solvent–
solute(CDC) interaction can be expected, the CDC may disso-
ciate quickly and only show the spectra of the superposition of
S-205 and bisphenol A.
Solid State 13C-NMR Spectrum of CDC. The solid state
13C-NMR spectrum was measured using the CP/MAS tech-
nique to obtain structural information inherent to the solid
CDC. The spectrum is shown in Fig. 3. In addition to broad-
ening of the signals on the whole, a noticeable feature specific
to the solid state 13C-NMR spectrum is the disappearance of
the spiro-carbon atom signal (C9 carbon), whose peak was
found at around 84 ppm of the lactone form S-205 in solution
or in the solid state. A dipolar dephasing CP/MAS technique
was applied to enhance the signal of the C9 carbon, which en-
abled us to locate it at around 133 ppm. The chemical-shift
value of 133 ppm is consistent with the idea that the carbon
atom is in the sp2 hybridized state.
Fig. 3. CP/MAS 13C-NMR spectrum of S-205 + Bisphenol
A Color Developing Complex (CDC).
The Other Attempts for Spectral Analyses. Other
at-
tempts, including (1) 1H-NMR measurements of CDC in solu-
tion, (2) UV-vis spectrum analyses of CDC in solution, and (3)
FAB (Fast Atom Bombardment) Mass measurement of CDC
in a more hydrophobic m-nitrobenzyl alcohol matrix, turned
out to be unsuccessful in terms of obtaining additional struc-
tural information inherent to CDC. In all of the above cases,
solutions and matrices became colorless before and during the
measurements, suggesting the spontaneous dissociation of
CDC to its component molecules. All experimental results in
solution and with FAB Mass measurements proved the fragile
character of CDC, which, together with the color reduction
phenomenon of CDC at elevated temperatures, particularly
under high humidity, agrees very well with the color unstabili-
ty observed on thermal paper (thermal paper was notorious for

Y. Takahashi et al.
Bull. Chem. Soc. Jpn., 75, No. 10 (2002) 2229
its low image persistence). A clue concerning with the chemi-
cal species of a black-color image developed on thermal paper
was obtained from reflection UV-vis measurements of CDC.
The reflection UV-vis spectrum of a black-color image (CDC)
on S-205 + bisphenol A thermal paper (Fig. 4) showed ab-
sorption maxima at λmax = 468 nm and 580 nm. These two ab-
sorption peaks were essentially the same as those in the spec-
trum of the solution of S-205 in 2,2,2-trifluoroethanol (Fig. 5).
In the latter case, the color formation was assigned to be a
zwitterionic form of S-2058,9 stabilized by an ample amount of
Fig. 4. Reflection UV-vis spectrum of black-color image developed on a thermal paper composed of S-205 and bisphenol A.
Magnitude of black-color developing was dependent on added thermal energy on a printer head. Added energy (mW) for each
scan (A, B, C, D) was 10, 6, 5, 4 mW, respectively.
Fig. 5. UV-vis solution spectra of S-205 (4.15 × 10−5 mol dm−3) in 2,2,2-trifluoroethanol and S-205 (1.71 × 10−5 mol dm−3) + tri-
fluoroacetic acid (1.20 × 10−3 mol dm−3) in CH3CN.

2230 Bull. Chem. Soc. Jpn., 75, No. 10 (2002)
Color Developing Phenomenon on Thermal Paper
2,2,2-trifluoroethanol surrounding S-205. This spectral agree-
ment strongly suggests that a basic chromophore responsible
for the color formation in solutions and in the solid state is the
same, and is a zwitterionic form of the fluoran dye that is stabi-
lized by hydrogen bond formation.
which was reported to be around −42 to −54 kJ/mol. These
figures can rationalize our proposal of CDC formation and iso-
lation under our experimental conditions.10
CDC is a fragile complex susceptible to a solvent with high
polarity, heat and humidity, which is in extremely good agree-
ment with the actual behavior of the images on thermal paper.
This, along with matching IR spectra of the image portion on
the thermal paper with that of CDC, supports well an idea that
CDC is indeed responsible for color formation on thermal pa-
per.
What Is Black Powder Composed of S-205 and Bisphe-
nol A? The prepared black solid was proved by both HPLC
and 1H-NMR measurements to be a complex (CDC) having a
definite molar ratio of 1:4 (S-205:bisphenol A), regardless of
the preparation conditions. In CDC, the dye molecule S-205
takes a zwitterionic structure where a cation is mainly located
at C9 (spiro-carbon) and an anion is on a carboxyl group. This
was deduced by IR and 13C-NMR spectroscopy. It should be
noted here that the same IR spectra can be obtained by heating
and melting a mixture of the fluoran dye and bisphenol A,
which takes place on actual thermal paper when an image is
thermally formed. These findings lead us to deduce that this
black solid is indeed CDC, which is the origin of color forma-
tion and is composed of fluorane dye and bisphenol A. Al-
though there is no direct proof, it is quite natural to assume that
the hydrogen bonding between the zwitterionic structure of S-
205 (acceptor) and bisphenol A (donor) acts as a major source
of complex stability (Scheme 2). This can agree well with the
findings that CDC loses its color easily in solvents with a hy-
drogen-bonding (either donor or acceptor) character. The role
of hydrogen bonding in color formation between a fluoran dye
and phenols was also suggested by Tokita et al.,9 where they
measured the 13C-NMR spectra of a fluoran dye dissolved in
liquid phenols at elevated temperatures. By monitoring the
UV-vis peak intensities of the absorption maxima around 450
and 590 nm by changing the experimental temperature of the
measurements, they evaluated the enthalpy gain by the hydro-
gen-bonding formation under their experimental conditions,
Conclusion
We successfully prepared and isolated a color-developing
complex between a fluoran dye and a phenol dye developer.
By measuring the IR and 13C-NMR spectra in solution and in a
solid form, we deduced that CDC is composed of one mole-
cule of a zwitterionic form of the dye and four molecules of
bisphenol A. Chemical analyses proved that CDC is a meta-
stable complex, and vulnerable to a solvent, prolonged heating,
and solvents with high polarity, which is in extremely good
agreement with the behavior of images on thermal paper.
Based on this CDC color-developing mechanism, which is a
departure from the conventional acid-base mechanism, we
have extended our work into the design of completely new dye
developers, the result of which will soon be reported.
Experimental
S-205 and the color developer bisphenol A were commercially
available. S-205 was obtained from Yamada Chemical. Color-de-
veloping experiments and the preparation of the Color Developing
Complex (CDC) were carried out using these commercially avail-
able compounds. The purity of the compounds was checked by
measuring the melting point (S-205; 164 – 166.5 °C, bisphenol
A; 158 – 159 °C). First, 0.52 g (1 mmol) of S-205 was dis-
solved in hot toluene (nearly boiling), to which 0.23 g (1 mmol) to
1.37 g (6 mmol) of bisphenol A was added and further heated to
obtain a clear solution. This solution was placed in an ice bath,
which lead to black precipitation formation at the bottom. This
was rapidly collected and filtered with suction. The black solid
was then washed a couple of times with cold toluene, and immedi-
ately placed together with filter paper in vacuo overnight. CDC
was most easily available when a starting molar ratio of 1:2 was
chosen.
UV-vis spectra were measured on a JASCOUVIDEC 610C UV-
vis spectrophotometer. Reflection UV-vis spectra were taken on
an MCPD 100 spectrophotometer (Otsuka Electronics). IR spec-
tra were recorded by a Perkin Elmer FT/IR Spectrum 2000 spec-
trometer. Solution 1H-, and 13C-NMR measurements were carried
out by a JEOL JNM-EX270 spectrometer in CD3CN at 25 °C with
reference to the (CH3)4Si standard. The NMR signal assignments
were performed completely by using C,H-COSY and the 2D-NOE
NMR technique. Solid state 13C-NMR spectra (CP/MAS) of
CDC were also measured on a Chemagnetics CMX-400 Infinity
Spectrometer (13C resonance frequency; 100MHz) with TOSS
(Total Suppression of Sidebands) and Dipolar Dephasing pulse
techniques. The dipolar dephasing CP/MAS technique is very ef-
fective to distinguish those carbon atoms with no attached hydro-
gen from other hydrogen attached carbons. FAB MS (Fast Atom
Bombardment Mass Spectrometry) experiments were carried out
on a JEOL JMS-AX500 mass spectrometer in m-nitrobenzyl alco-
Scheme 2.

Y. Takahashi et al.
Bull. Chem. Soc. Jpn., 75, No. 10 (2002) 2231
hol matrix.
can interact with these electron rich atoms in S-205 and form a
1:4 complex stabilized by the hydrogen bond. Further investiga-
tion is needed to clarify the structure of CDC. We are now in the
process to get further structural information on CDC, and to eluci-
date the mechanism how the CDC is formed with a definite molar
ratio.
The authors express their appreciation to Professor
Toshimichi Fujiwara, Osaka University, and Professor Hiroko
Suezawa, Yokohama National University, for their technical
advice and great help to measure the solid state NMR and solu-
tion NMR spectra. The authors also thank Dr. Takeo Kaneko
for his repeated attempts to measure the FAB Mass spectra of
CDC.
7
E. Breitmaier and W. Voelter, in “13C NMR Spectroscopy,
Methods and Applications in Organic Chemistry,” 2nd ed, Velrag
Chemie Weinheim, New York (1978), pp. 110–114.
8
D. A. Hinckley and P. G. Seybold, Spectrochim. Acta, Part
A, 44, 1053 (1988).
References
9
M. Yanagida, I. Aoki, and S. Tokita, Bull. Chem. Soc. Jpn.,
70, 2757 (1997).
1
2
H. H. Baum (NCR co.), U.S. Patent 3451338 (1969).
N. Yamato, J. of the Institute of Image Electronics
10 The barrier between (L; colorless lactone form) and (Z;
black colored zwitterion form) forms of the fluorane compounds
can be estimated approximately from the Eyring equation to cor-
relate the rate constant (k1) for the equilibrium and the activation
free energy (∆G ).
Engineers of Japan, 4, 185 (1975).
C. H. Rochester, “The Chemistry of the Hydroxyl Group,”
Part 1, ed by S. Patai, Interscience, New York (1971), Chap. 7, P.
374.
3
k1 = k (kT / h) exp(−∆G )
(A)
4
L. J. Bellamy, in “The Infra-red Spectra of Complex
Molecules,” Chapman and Hall, London, 184 (1975).
J. Sueyoshi, M. Kubata, H. Yoshida, K. Nakatsu, and Y.
where, k is transmission coefficient, h is Plank constant, and T is
absolute temperature.
5
If we assume the half-life period (t) to distinguish the (L) and (Z)
forms separetely is 1 day (86400 seconds) at ambient temperature,
the rate constant k1 can be calculated approximately to be 0.8 ×
10−5 s−1 by using the following equation.
Hatano, Chem. Funct. Dyes, Proc. Int. Symp., 2nd , Mita Press,
Tokyo, Japan (1993), P. 34.
6
At present, it is not clear why CDC can be formed with a
definite molar ratio (S-205:bisphenol A = 1:4). Preliminary
semi-empirical molecular orbital calculations on the open-form of
S-205 suggest that there exist four electron rich atoms which can
function as proton acceptors (two carboxylate oxygen atoms and 2
alkylamino nitrogen atoms) in a molecule. It may reasonable to
think that each hydroxy proton from four bisphenol A molecules
t = (ln2) / k1
(B)
And then, obtained k1 value and other necessary values as as-
sumed k = 1, T = 293 K were put into the Eq. A to give ∆G value
as about 100 kJ/ mol.