Kinetics and mechanisms of hydrolysis of tetraphenylporphyrins tethered to silicate glass via a primary or tertiary alcohol linker

Article abstract of DOI:10.1016/j.tet.2014.05.007

Tetraphenylporphyrins carrying primary or tertiary alcohols in a phenyl group were bonded to silicate glass by heat treatment. The rate of base catalyzed hydrolysis of tertiary ester was 20 times slower than that of primary ester, while the rate of acid catalyzed hydrolysis of tertiary ester was only 2.5 times slower than that of primary ester. Hydrolysis of tertiary alcohol bonded silica in HCl/HO displayed that there is a covalent bond between alcohol oxygen and silicon, and the C-O bond is cleaved under acidic conditions, while the Si-O bond is cleaved under basic conditions.

Full text of DOI:10.1016/j.tet.2014.05.007

Tetrahedron xxx (2014) 1e7
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Kinetics and mechanisms of hydrolysis of tetraphenylporphyrins
tethered to silicate glass via a primary or tertiary alcohol linker
*
Nao Furuta, Takaaki Yagi, Tadashi Mizutani
Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, and Center for Nanoscience Research, Doshisha University,
Kyotanabe, Kyoto 610-0321, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Tetraphenylporphyrins carrying primary or tertiary alcohols in a phenyl group were bonded to silicate
glass by heat treatment. The rate of base catalyzed hydrolysis of tertiary ester was 20 times slower than
that of primary ester, while the rate of acid catalyzed hydrolysis of tertiary ester was only 2.5 times
slower than that of primary ester. Hydrolysis of tertiary alcohol bonded silica in HCl/H218O displayed that
there is a covalent bond between alcohol oxygen and silicon, and the CeO bond is cleaved under acidic
conditions, while the SieO bond is cleaved under basic conditions.
Received 17 April 2014
Received in revised form 2 May 2014
Accepted 4 May 2014
Available online xxx
Keywords:
Tertiary alcohol
Porphyrin
Ó 2014 Elsevier Ltd. All rights reserved.
Silicate glass
Silyl ester
Hydrolysis
Mechanism
1. Introduction
Kitahara reported that the forward reaction of Eq. 1 proceeded
sluggishly when tert-butyl alcohol was used: the number of alkoxy
2
ꢀ
The interconversion between silanols (hydroxysilanes) and
alkoxysilanes (Eq. 1) is a key reaction in a number of practically
important processes, such as solegel synthesis of ceramics,1 surface
modification of silicate glass or silica gel,2 and silyl protection/
deprotection of OH groups in organic synthesis.3
groups per 100 A of n-butyl alcohol bonded silica gel was 3.2
while that of tert-butyl alcohol was 0.7.6 Hasegawa and Sakka
reported that transesterification shown in Eq. 2 proceeds in the
presence of cation-exchange resin in the proton form for all iso-
mers of butanol, and only tert-butanol unexpectedly gave a re-
active silanol species.7
hSi ꢀ OH þ ROH % hSi ꢀ OR þ H2O
(1)
hSi ꢀ OR þ R0OH %hSi ꢀ OR0 þ ROH
Peculiar reactivities of tertiary alcohols have been reported,
while the molecular mechanisms behind the reactivities are not
well known.
(2)
Surface reactions and adsorption on silicate or other metal
oxides are applied to catalysis, separation science, microelectron-
ics and composite materials. Elucidation of the stability of silyl
ester bonds and the mechanism of their reactions can extend
applicability of the thin film of alcohols on metal oxides to various
fields of chemistry and materials science. In this paper, we focus
on the reactions between surface silanols on solid silicon oxide
and alcohols. In most studies on reactions of silanols on solid
surface, primary alcohols have been used, such as methanol, eth-
anol, and butanol. There are a few reports employing tertiary al-
cohol.4 Lambert and Singer5 reported that chemisorption
reactivity of pentanol isomers toward thermally activated silica
decreases in the order: normal>iso>secondary>neo>tertiary.
We report herein comparative studies on the forward and
backward reactions of Eqs. 1 and 2 on silicate glass or silica gel
employing primary alcohol and tertiary alcohol bearing a porphyrin
chromophore. Both primary alcohol and tertiary alcohol reacted
with silanol groups on silicate glass to afford alcohol bonded silicate
glass. Tertiary alcohol bonded silicate glass was resistant against
base catalyzed hydrolysis compared to primary alcohol bonded
silicate glass. We found that the acid catalyzed solvolysis (Eqs. 1 and
2) of tertiary alcohol bonded silicate proceeded through CeO bond
scission, while the base catalyzed solvolysis reaction of primary and
tertiary alcohol bonded silicate as well as the acid catalyzed sol-
volysis reaction of primary alcohol bonded silicate all proceeded
through SieO bond scission.
* Corresponding author. Tel.: þ81 774 65 6623; fax: þ81 774 6794; e-mail ad-
dress: tmizutan@mail.doshisha.ac.jp (T. Mizutani).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.05.007
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
2. Results and discussion
2.1. Preparation of porphyrin alcohols
Three alcohols bearing a porphyrin chromophore 1, 2, and 3
were prepared to compare influence of the alcohol structures on
the forward and backward reactions of Eq. 1. Monolayers of por-
phyrin on silicate glass can be easily detected with electronic ab-
sorption spectroscopy owing to the large molar absorptivity of
porphyrin in the visible region, so that kinetic studies were feasible.
Alcohol 1 was prepared by the Williamson ether synthesis reaction
of 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin with 5-
bromopentyl acetate followed by alkaline hydrolysis of the ester.8
Alcohol 2 was obtained by the Williamson ether synthesis re-
action of the same porphyrin with methyl 5-bromopentanoate,
followed by the reaction with the methyl Grignard reagent. Alcohol
3 was prepared by the ether synthesis reaction of the same por-
phyrin with methyl 5-bromo-2-ethylpentanoate, followed by re-
duction with LiAlH4. Alcohols 1, 2, and 3 were characterized with 1H
NMR and MALDI-TOF mass spectroscopy (Supplementary data)
(Chart 1).
Fig. 2. Plots of absorbances at the Soret band of UVevisible spectra of 2 bonded silicate
glass against time.
absorbances increased as the reaction time was longer and satu-
rated when the temperature was high. The absorbances of 1 or 2
bonded glass were saturated at 0.07 and 0.06, respectively. The
amounts of porphyrins bonded to silicate glass was determined by
immersing the silicate glass in 0.1 M NaOH at 50 ꢁC for 30 min, and
Chart 1.
2.2. Reaction of alcohols with silicate glass
the amounts of desorbed porphyrin was spectrophotometrically
determined.8 The amounts of porphyrins 1 and 2 adsorbed on sil-
icate glass were 1.8ꢂ1014 and 1.4ꢂ1014 molecules/cm2, respectively.
Therefore, tertiary alcohol reacted slower than primary alcohol,
while the adsorbed amount of tertiary alcohol was not much
smaller than that of primary alcohol. The Langmuir rate constant9
at 180 ꢁC for formation of 1 bonded silicate glass was 0.012 minꢀ1
while that for 2 was 0.0058 minꢀ1, indicating that tertiary alcohol 2
reacted ca. two times slower than primary alcohol 1. The amount of
bonded 2 was much smaller than 1 at temperatures below 160 ꢁC,
consistent with reported low reactivity of tert-alcohol at 55 ꢁC to-
ward thermally activated silica gel.5
Alcohols 1 and 2 were spin-coated on silicate glass and heated at
80e240 ꢁC for up to 5 h. Washing with chloroform to remove
unreacted alcohols afforded the alcohol bonded silicate glass. Figs.1
and 2 show plots of absorbance at the Soret band of the glass
against reaction time for various reaction temperatures. The
2.3. Kinetic studies on hydrolysis of alcohol-bonded silica
Alcohol 1 and 2 bonded silicate glass was immersed in 1 M
aq HCl at 50 ꢁC or in 1 M aq NH3 at 30 ꢁC and progress of hydrolysis
was monitored by recording UVevisible spectra of the glass after
washing it with CHCl3. The progress of hydrolysis under acidic
conditions is shown in Fig. 3. Comparison of the half-life of the
reaction showed that hydrolysis of 2 in HCl was ca. 2.5 times slower
than that of 1. It is interesting to note that the progress of acid-
catalyzed hydrolysis did not follow a simple first-order kinetic
model. There seem to be fast and slow fractions owing to
Fig. 1. Plots of absorbances at the Soret band of UVevisible spectra of 1 bonded silicate
glass against time.
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
3
inhomogeneous solid surface. Incomplete acid hydrolysis of alco-
hols on silicate glass was also observed for other hydrox-
yporphyrins.8 The progress of hydrolysis can be fit to the double
exponential function:
Fig. 4. Absorbance changes at the Soret band during the reactions of 1, 2, and 3 bonded
silicate glass with 1 M aq NH3 at 30 ꢁC. Curves represent the simulated absorbance
changes due to the first-order kinetics with kobs¼3.4ꢃ0.2 hꢀ1 for 1, 0.17ꢃ0.007 hꢀ1 for
2 and, 1.89ꢃ0.05 hꢀ1 for 3. UVevisible spectra were recorded after washing with
CHCl3.
Table 2
Fig. 3. Absorbance changes at the Soret band during the reactions of 1, 2, and 3 on
silicate glass with 1 M aq HCl at 50 ꢁC. UVevisible spectra were recorded after washing
with CHCl3.
The first-order rate constants of hydrolysis of 1, 2, and 3 bonded silicate glass in 1 M
aq NH3 at 30 ꢁC
k/hꢀ1
1
2
3
3.4ꢃ0.2
A ¼ peꢀk t þ ð1 ꢀ pÞeꢀk t
(3)
1
2
0.17ꢃ0.007
1.85ꢃ0.05
where A represents the normalized absorbance at time t, k1 and k2
are the rate constants of hydrolysis of labile and inert silicate ester,
respectively, and p is the fraction of the labile silicate ester. Table 1
lists the kinetic parameters. The labile fraction p of tertiary alcohol
2 bonded silicate glass was much smaller than that of primary al-
cohol 1 bonded silicate glass. Branched primary alcohol with steric
hindrance 3 also showed a smaller p value. Therefore steric hin-
drance seems to increase the inert fraction of silicate ester on sili-
cate glass.
hydrolysis were reported by Shirai et al.:11 they found that hydro-
lysis of tert-butoxytrimethylsilane in acidic aq acetone at 37 ꢁC
proceeded seven times slower than benzyloxytrimethylsilane,
while hydrolysis in basic media proceeded 9600 times slower.
2.4. Mechanism of solvolysis of alcohol-bonded silica
In order to gain more insights into the mechanism of hydrolysis,
we performed the acid or base catalyzed ethanolysis of 1 and 2
bonded silica gel and the products were characterized by MALDI-
TOF mass spectroscopy. We used silica gel instead of silicate glass
to obtain enough amounts of products for mass spectroscopic
analysis. The reaction of 2 bonded silica gel in 0.1 M HCl in ethanol
at 50 ꢁC yielded several products. They were separated with silica
gel chromatography and the molar ratios of each product were
determined with UVevisible spectroscopy. The products were ethyl
ether 4, alkene 5, and alcohol 2 in a molar ratio of 44:44:12 (for the
structures of the products, see Scheme 1). We confirmed that nei-
ther ether 4 nor alkene 5 was detected with mass spectroscopy
after heating a solution of 2 in 0.1 M HCl in ethanol at 50 ꢁC in the
presence of silica gel or in the absence of silica gel. Therefore, for-
mation of 4 and 5 was not due to the aging of a solution of 2 under
acidic conditions. We also carried out hydrolysis of 2 bonded silica
Table 1
Kinetic parameters of acid hydrolysis of 1e3 bonded silicate glass
k1/minꢀ1
k2/minꢀ1
p (fraction of labile component)
1a
2
3
(7.6ꢃ1.5)ꢂ10ꢀ2
(7.7ꢃ1.7)ꢂ10ꢀ2
(7.5ꢃ0.02)ꢂ10ꢀ2
(8.1ꢃ1.4)ꢂ10ꢀ4
(1.6ꢃ0.05)ꢂ10ꢀ3
(8.6ꢃ0.9)ꢂ10ꢀ4
0.42ꢃ0.02
0.16ꢃ0.02
0.26ꢃ0.02
a
Taken from literature.8
Fig. 4 shows the progress of hydrolysis in 1 M aq NH3 of 1, 2, and
3 bonded silicate glass at 30 ꢁC. Decrease in absorbance was fit to
the first-order kinetic decay: Abs/Abs0¼eꢀkt. The rate constant for 2
was determined with the data up to 6 h, since decrease in absor-
bance after 6 h was faster than expected from the first order ki-
netics. The first-order rate constants are listed in Table 2. Hydrolysis
of 2 in 1 M aq NH3 was 20 times slower than 1. Sterically hindered
primary alcohol 3 showed ca. two times slower hydrolysis than
primary alcohol 1. Steric effects seem to be important in hydrolysis,
particularly under basic conditions. Interestingly, the primary al-
cohol with a branched chain 3 showed relatively fast hydrolysis,
indicating that the tertiary structure of 2 is significant. Similar re-
tardation of hydrolysis due to steric effects has been reported for
tetraalkoxysilane10 and trialkylsiloxane11 in homogeneous solu-
tions and for alkoxylated silica12 in a heterogeneous system. En-
hanced steric effects in alkaline hydrolysis compared to acid
18
gel in 0.1 M HCl in H2 O at 30 ꢁC for 24 h. The MALDI-TOF mass
spectrum of the product showed that the recovered 2 was almost
exclusively labeled with 18O (Fig. 5). Hydrolysis of 2 bonded silica
gel in 1 M HCl at 50 ꢁC for 24 h yielded not only alcohol 2 but also
alkene 5. As a control experiment, a mixture of 2 and silica gel was
heated under the same conditions. The mass spectrum showed that
no 18O was introduced in 2 (dotted line, Fig. 5). These results
demonstrated that (1) tert-alcohol 2 was bonded to silica gel via
a covalent bond, and (2) acid solvolysis of tert-alcohol 2 bonded
silica gel proceeded through CeO bond scission. The solvolysis of
primary alcohol 1 bonded silica gel in 0.1 M HCl in ethanol afforded
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
Scheme 1. Reaction scheme of acid or base catalyzed solvolysis of primary or tertiary alkyl silicate glass.
It has been demonstrated that hydrolysis of silicate esters in
homogeneous solutions proceeds through SieO bond scission in-
stead of CeO bond scission by several lines of evidence, such as
isotope labeling studies using H218O.13 Silicon can form a penta-
coordinated intermediate so that the SieO bond is more labile than
the CeO bond.14,15 Utsugi et al. demonstrated that hydrolysis of the
chiral alcohol bonded silica proceeds through SieO bond scission
based on the optical activity of the hydrolyzed alcohol.16 We
demonstrated that acid solvolysis of tert-alcohol bonded silica
proceeded through CeO bond scission, indicating that the re-
activity of the tertiary CeO bond can be competitive with that of the
SieO bond under acidic conditions. The CeO bond scission of tert-
alcohol is consistent with the observation of (EtO)3SiOH formation
during acid-catalyzed transesterification of Si(OEt)4 and tert-butyl
alcohol.7 The slower rate of base hydrolysis of tertiary alcohol 2
bonded silica than that of primary alcohol 1 bonded silica can be
ascribed to the steric hindrance of the neighboring methyl groups
of 2 for nucleophilic attack of the OHꢀ ion to Si.
Fig. 5. MALDI-TOF MS of the product of acid hydrolysis of 2 bonded silica gel in 0.1 M
18
HCl in H2 O at 30 ꢁC for 24 h (solid line), and 2 deposited on silica gel in 0.1 M HCl in
18
H2 O at 30 ꢁC for 24 h (dotted line).
only alcohol 1 as a sole product. Solvolysis under basic conditions
gave completely different results. For the reaction of both 1 and 2
bonded silica gel in 0.1 M EtONa in ethanol afforded only the cor-
responding alcohols. Thus, solvolysis of 1 under acidic conditions
and solvolysis of 1 and 2 under basic conditions all proceeded
through SieO bond scission. Suggested reaction mechanisms of
acid-catalyzed and base-catalyzed solvolysis are summarized in
Scheme 2.
2.5. Mechanism of reaction of alcohol with silicate glass
The reaction mechanism of condensation of alcohols with sila-
nol on silica gel is not well understood, and previous studies fo-
cused on the effects of preheating of silica on the reaction with
alcohols.17 We prepared (18O)-2 bonded silica gel and subsequent
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
5
Scheme 2. Suggested reaction mechanisms of acid or base catalyzed solvolysis of primary or tertiary alkyl silicate glass.
solvolysis with NaOEt/EtOH yielded (18O)-2, as determined by
MALDI-TOF mass spectroscopy (Scheme 3). Therefore, condensa-
tion of 2 with silanol proceeded with attack of the alcohol oxygen to
Si. Formation of a carbenium ion intermediate was excluded even
for sterically crowded tert-alcohol.
In conclusion, we demonstrated that tert-alcohol was bonded to
silicate glass and silica gel by heating the spin-coated film of tert-
alcohol on silica. Alkaline hydrolysis of tert-alcohol bonded silica
was 20 times slower than primary alcohol, while acid hydrolysis of
tert-alcohol bonded silica was only 2.5 times slower than primary
Scheme 3. Reactions of condensation of (18O)-labeled tertiary alcohol with silanol groups on silicate glass followed by solvolysis in NaOEt/EtOH.
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
alcohol bonded silica. Solvolysis in H218O or in ethanol demon-
strated that acid catalyzed solvolysis of tert-alcohol bonded silica
proceeded through the CeO bond scission, contrary to generally
accepted mechanism of SieO bond scission.
3.5. Base catalyzed ethanolysis of porphyrin bonded silica gel
Porphyrin bonded silica gel dried at 50 ꢁC for 1 h in vacuo was
stirred in 0.1 M EtONa in EtOH (50 mL) at 50 ꢁC for 18 h under Ar.
The suspension was cooled to room temperature, followed by fil-
tration. The silica gel was washed with CHCl3 and acetone. The
filtrate was neutralized with 0.1 M HCl and CHCl3 was added. The
organic layer was separated and washed with saturated NaHCO3 aq
three times and H2O three times. The organic layer was dried over
Na2SO4 and evaporated in vacuo. The product was characterized by
MALDI-TOF mass spectroscopy.
3. Experimental section
3.1. Materials
Micro glass slide (76 mmꢂ26 mm) was purchased from Mat-
sunami Glass Ind., Ltd. The glass slides were immersed in a solution
of H2SO4/30% H2O2 (70:30, v/v) at 80 ꢁC for 1 h, washed with water,
bath-sonicated in water, and dried under N2 gas. H218O (ꢄ98 atom%
18O) was purchased from Taiyo Nippon Sanso Corp. 0.1 M and 1 M
HCl in H218O was prepared by addition 12 M HCl in H216O to H218O.
Melting points were determined by Shimadzu Differential Calo-
rimeter DSC-60. Silica gel, CARiACT Q-6, was purchased from Fuji
3.6. Acid catalyzed hydrolysis of porphyrin 2 bonded silica gel
in H218O
After (16O)-2 bonded silica gel was dried at 50 ꢁC for 1 h in vacuo,
18
it was stirred in 0.1 M HCl in H2 O (8 mL) at 30 ꢁC for 24 h under Ar.
Silysia Chemical Ltd. It had a specific surface area of 451 m2 ꢀ1. A
g
The suspension was cooled to room temperature and then it was
filtered. The silica gel was washed by CHCl3, acetone, and saturated
NaHCO3 aq. To the filtrate was added CHCl3 and washed with sat-
urated NaHCO3 aq three times and H2O three times. The organic
layer was dried over Na2SO4 and evaporated in vacuo. The product
was characterized by MALDI-TOF mass spectroscopy.
hot stage Mettler-Toledo FP82HT was used for heat treatment of the
spin-coated films. UVevisible spectra were obtained with a Per-
kineElmer Lambda 950 spectrophotometer. 1H NMR spectra were
recorded with a JEOL JNM-ECA500 spectrometer. Tetramethylsilane
was used as an internal standard. Matrix-assisted laser desorp-
tioneionization time-of-flight mass (MALDI-TOF MS) spectra were
recorded on a Bruker Daltonics Autoflex Speed spectrometer.
3.7. Preparation of 18O-labeled porphyrin 2 ((18O)-2)
3.2. Preparation of porphyrin 1e3 monolayers on silicate
glass
After (16O)-2 bonded silica gel was dried at 50 ꢁC for 1 h in vacuo,
18
it was stirred in 1 M HCl in H2 O (8 mL) at 50 ꢁC for 72 h under Ar.
A silicate glass was cleaned by immersion in a ‘piranha’ solution
(H2SO4:30% H2O2¼70:30 (v/v)) for 1 h at 80 ꢁC. After being cooled
to room temperature, it was rinsed with ultrapure water, filtered
with a MilliQ system from Millipore and then sonicated in ultrapure
water. Then it was dried in a N2 stream. A CHCl3 solution of 1e3
The suspension was cooled to room temperature and then it was
filtered. The silica gel was washed by CHCl3, acetone, and saturated
NaHCO3 aq. To the filtrate was added CHCl3 and washed with sat-
urated NaHCO3 aq three times and H2O three times. The organic
layer was dried over Na2SO4 and evaporated in vacuo. The product
was analyzed by MALDI-TOF mass spectroscopy to confirm that
18O-labeled porphyrin 2 was obtained.
(60 mL, 4.2 mM) was spin-coated on the silicate glass at 3000 rpm
for 60 s. The spin-coated film was then heated on a hot stage at
80e240 ꢁC for 5 min to 5 h to allow a condensation reaction to
proceed. The silicate glass was washed with CHCl3 to remove
unreacted porphyrins. The resultant glass adsorbing porphyrin was
analyzed by UVevisible spectroscopy.
3.8. Acid catalyzed reaction of porphyrin 2 in the presence of
SiO2 gel in EtOH or H218O
Porphyrin 2 (3.72 mg) was dissolved in CHCl3 (5 mL), and silica
gel (50 mg), which had been dried at 100 ꢁC for 1 h in vacuo, was
added to the CHCl3 solution. Evaporation of the CHCl3 gave silica gel
with porphyrin 2 deposited on the surface. Under Ar, the 2 phys-
isorbed on SiO2 gel was stirred in 0.1 M HCl in EtOH (50 mL) at 50 ꢁC
3.3. Preparation of porphyrins 1 or 2 bonded silica gel
Porphyrin (1: 3.59 mg or 2: 3.72 mg) was dissolved in CHCl3
(5 mL) and silica gel (50 mg) dried at 100 ꢁC for 1 h in vacuo was
added to the CHCl3 solution. After evaporation of the CHCl3, the
silica gel was heated at 160 ꢁC (for 1) or 200 ꢁC (for 2) for 4 h. The
silica gel was cooled to room temperature and then washed in
CHCl3 in a bath sonicator to remove unreacted porphyrins. The red
silica gel was collected by suction filtration and dried in vacuo. The
resultant silica gel was subjected to the studies of hydrolysis and
ethanolysis.
18
for 18 h or in 0.1 M H2 O (8 mL) at 30 ꢁC for 24 h. After the sus-
pension was cooled to room temperature, it was filtered. The silica
gel was washed with CHCl3, acetone and saturated NaHCO3 aq. To
the filtrate was added CHCl3 and washed with saturated NaHCO3 aq
three times and H2O three times. The organic layer was dried over
Na2SO4 and evaporated in vacuo. The product was characterized by
MALDI-TOF mass spectroscopy.
3.4. Acid catalyzed ethanolysis of porphyrin bonded silica gel
3.9. Acid catalyzed reaction of porphyrin 2 in the absence of
SiO2 gel in EtOH
Porphyrin bonded silica gel dried at 50 ꢁC for 1 h in vacuo was
stirred in 0.1 M HCl in EtOH (50 mL) at 50 ꢁC for 18 h under Ar. After
cooling the suspension to room temperature, it was filtered and the
silica gel was washed with CHCl3, acetone, and saturated NaHCO3
aq. To the filtrate was added CHCl3, and the organic layer was
separated and washed with saturated NaHCO3 aq three times and
with H2O three times. The organic layer was dried over Na2SO4 and
evaporated in vacuo and the products were characterized by
MALDI-TOF mass spectroscopy.
Porphyrin 2 (3.72 mg) was dissolved in 0.1 M HCl in EtOH
(50 mL) and the solution was stirred at 50 ꢁC for 18 h under Ar. It
was cooled to room temperature, followed by adding CHCl3
(50 mL). The organic layer was washed with saturated NaHCO3 aq
three times and H2O three times. The organic layer was dried over
Na2SO4 and the solvents were evaporated in vacuo. The product
was characterized by MALDI-TOF mass spectroscopy.
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N. Furuta et al. / Tetrahedron xxx (2014) 1e7
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3.10. Synthesis of porphyrins 1e3
See Supplementary data.
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available. Supplementary data related to this article can be found at
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Please cite this article in press as: Furuta, N.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.05.007