Transesterification of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate with tetrakis(hydroxymethyl)methane. the properties of the reaction products

Article abstract of DOI:10.1007/s11172-012-0234-z

The transesterification of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate with tetrakis(hydroxymethyl)methane depends on the equilibrium constants of the reversible reactions; for the final step, the equilibrium constant is K 1. The molecular geometries and the enthalpies and entropies of the equilibrium reactions were calculated by the semiempirical PM6 quantum chemical method. The thermodynamic equilibrium constants of the reversible reactions were calculated by the Boltzmann equation from the Gibbs energies G _f ^○. For tris-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoyloxymethyl](hydroxymethyl)methane, the dipole moment is μ = 0.97 D and the energy of the O-H homolysis is D _OH = 347.3 kJ mol ^-1. For tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoyloxymethyl]methane, μ is 5.6 D and D _OH is 321 kJ mol ^-1. The geometry of the structure affects the H-O homolysis energy and the chain termination coefficient under the conditions of inhibited cumene oxidation.

Full text of DOI:10.1007/s11172-012-0234-z

Russian Chemical Bulletin, International Edition, Vol. 61, No. 9, pp. 1689—1693, September, 2012
1689
Transesterification of methyl 3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoate
with tetrakis(hydroxymethyl)methane. The properties of the reaction products
A. A. Volod´kin, G. E. Zaikov, and N. M. Evteeva
N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences,
4 ul. Kosygina, 119991 Moscow, Russian Federation.
Fax: +7 (499) 137 4101. Eꢀmail: chembio@sky.chph.ras.ru
The transesterification of methyl 3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoate with
tetrakis(hydroxymethyl)methane depends on the equilibrium constants of the reversible reacꢀ
tions; for the final step, the equilibrium constant is K << 1. The molecular geometries and the
enthalpies and entropies of the equilibrium reactions were calculated by the semiempirical
PM6 quantum chemical method. The thermodynamic equilibrium constants of the reversible
reactions were calculated by the Boltzmann equation from the Gibbs energies Gf. For trisꢀ
[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxymethyl](hydroxymethyl)methane, the diꢀ
pole moment is  = 0.97 D and the energy of the O—H homolysis is DOH = 347.3 kJ mol–1. For
tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxymethyl]methane,  is 5.6 D and
DOH is 321 kJ mol–1. The geometry of the structure affects the H—O homolysis energy and the
chain termination coefficient under the conditions of inhibited cumene oxidation.
Key words: methyl 3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoate, tetrakis[3ꢀ(3,5ꢀdiꢀ
tertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxymethyl]methane, transesterification, quantum chemꢀ
ical calculations, PM6 level, structure, equilibrium, NMR spectra, IR spectra.
The results of the transesterification of methyl 3ꢀ(3,5ꢀ
diꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoate with polyols
are known and generalized in reviews.1,2 However, inforꢀ
mation on the synthesis of tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀ
hydroxyphenyl)propanoyloxymethyl]methane is inconsisꢀ
tent, mainly referring to patent data.3—7 A reaction with
tetrakis(hydroxymethyl)methane is step transesterification
leading to four compounds, the yields and ratio of which
vary with time. Tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyꢀ
phenyl)propanoyloxymethyl]methane (phenozanꢀ23)1,7
is an efficient antioxidant used to prepare polymeric
products.
Interest in the transesterification reaction is due to the
development of methods for the synthesis of phenozanꢀ23.
During the reaction, the increasing viscosity negatively
affects the reaction outcome and necessitates a temperaꢀ
ture raise above 120 C. However, baseꢀcatalyzed transesꢀ
terification at high temperatures is accompanied by oxiꢀ
dation and degradation processes, which complicates isoꢀ
lation and purification of the target product. The mechaꢀ
nism of the step transesterification remains unknown so far,
nor are data available regarding the effect of intermediate
products on the "consumer" properties of phenozanꢀ23.
In the present work, we revealed the rules governing
the transesterification, obtained bis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ
4ꢀhydroxyphenyl)propanoyloxymethyl]bis(hydroxymethꢀ
yl)methane and tris[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenꢀ
yl)propanoyloxymethyl](hydroxymethyl)methane, and
studied their antioxidant properties in inhibited oxidation
of cumene as a model reaction. Quantum chemical calcuꢀ
lations of the starting reagents, intermediates, and final
products in the transesterification at the PM6 level were
used to determine the thermodynamic equilibrium conꢀ
stants and the binding energies of the phenolic H—O bond
(DOH). The structures of the compounds obtained were
confirmed by 1H NMR and IR spectroscopy.
The methodology of the preparation of tetra[3ꢀ(3,5ꢀ
diꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxymethyl]ꢀ
methane depends on the conditions of methanol separaꢀ
tion in the final transesterification step, which has an
abnormally low equilibrium constant. Under the transesꢀ
terification conditions, the timeꢀdependent partition of
methanol in the liquid—gas system changes the reacꢀ
tion rates.
Results and Discussion
A reaction of methyl 3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyꢀ
phenyl)propanoate (1) with tetrakis(hydroxymethyl)ꢀ
methane at 140—200 C was accompanied by liberation
of methanol. Under these conditions, the final mixture
contained the starting compound 1 and transesterification
products 2—5 (Scheme 1).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1673—1677, September, 2012.
1066ꢀ5285/12/6109ꢀ1689 © 2012 Springer Science+Business Media, Inc.

1690
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 9, September, 2012
Volod´kin et al.
Scheme 1
Ci/mol L–1
100
80
60
40
20
0
1
5
4
3
0
20
40
60
80
100 /min
Fig. 1. Changes in the concentrations Ci of the reactants (i = 1,
3—5) during the transesterification of compound 1 with tetraꢀ
kis(hydroxymethyl)methane at 190 C; the initial molar ratio of
the reactants is 4 : 1; aluminosilicate modified with NaOH
(4.5 wt.%) as a catalyst.
The enthalpies Hf and entropies Sf of formation of the
compounds involved in the transesterification were calculatꢀ
ed at the PM6 level with the MOPAC 2009 program,8 and the
results obtained were used to calculate the Gibbs energy
changes Gr in reversible reactions (1)—(4) (Tables 1, 2).
The formation of compound 5 in reaction (4) involves
the most considerable decrease in the entropy, which probꢀ
ably accounts for its high reactivity in inhibited oxidation
reactions.
The compositions of the reaction mixtures were examꢀ
ined by LC and NMR spectroscopy. Compounds 3—5
were isolated in the individual state; their structures were
confirmed by 1H NMR and IR spectra. The ratio of comꢀ
pounds 1—5 in the reaction mixtures was determined from
the integral intensities of the signals for the methyl proꢀ
tons in COOMe ( 3.70 (1)) and for the methylene proꢀ
tons in COOCH2 ( 4.04 (3), 4.01 (4), and 4.09 (5)).
The 1H NMR spectra of compounds 3 and 4 show
signals for the protons of the group CH2OH. When the
ratio of 1 : tetrakis(hydroxymethyl)methane is 4 : 1, the
yield of compound 2 under the transesterification condiꢀ
tions does not exceed 3—4%. Liquid chromatography data
for the reaction mixtures agree with their 1H NMR spectra.
According to kinetic data, the liquid phase of the system
liberating methanol at P = 1 atm and 190 C reaches equiꢀ
librium 40—50 min after the start of the reaction. During
the next hour, the concentration of compound 4 (C4) passes
through a maximum, while the concentration of comꢀ
pound 5 (C5) increases (Fig. 1).
Table 1. PM6ꢀcalculated enthalpies Hf and entroꢀ
pies Sf of formation of the compounds at 298 K
Compound
Hf
Sf
/kJ mol–1
/J K–1 mol–1
PET*
1
33.0
67.9
437
713
2
89.7
869
3
4
5
147.1
206.6
261.9
11.5
1299
1773
2170
240
MeOH
* PET is tetrakis(hydroxymethyl)methane.
The ratio of compounds 4 and 5 remains the same even
when methanol is removed in vacuo. This can be attributꢀ
ed to the effect of the equilibrium constants of the reversꢀ
ible reactions on the final outcome of the step transeꢀ
sterification. Quantum chemical calculations gave K4 =
= 1.6•10–4 (298 K) for the thermodynamic equilibrium
constant of reaction (4). It is wise to assume that
the equilibrium in the system 5—4—MeOH is shifted
toward to the formation of compound 4. Reverse transꢀ
esterification in a reaction of compound 5 with methanꢀ
ol proceeded at room temperature to give the starting
compound 1.
Table 2. PM6ꢀcalculated changes in the enthalpy (Hr), entroꢀ
py (Sr), and Gibbs energy (Gr) for reactions (1)—(4) at 298 K
Reacꢀ
tion
Hr
Gr
Sr
Equilibrium
constant
J K–1 mol–1
kJ mol–1
1
2
3
4
0.3
1.0
3.1
12.5
13.8
2.8
–41
–43
1
К1 = 6.4•10–3
К2 = 3.8•10–3
К3 = 3.2•10–1
К4 = 1.6•10–4
–1.1
21.6
–76

Transesterification of 3,5ꢀBut2ꢀ4ꢀHOC6H2CH2CH2COOMe
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 9, September, 2012
1691
Table 4. PM6ꢀcalculated distances between the
phenolic O atoms in structures 4 and 5
The O—H homolysis energy DOH is an indicator of the
antioxidant efficiency of phenol derivatives. The DOH valꢀ
ues can be calculated from the energies of formation of
phenol (EfInH) and the corresponding phenoxyl radical
(EfIn•) from the atoms and the energy of formation of the
Distance
d/Å
4
5
H atom by dissociation of molecular hydrogen (EH
=
= 218.0 kJ mol–1). The calculated energies of formation
of compounds 1—5 and their phenoxyl radicals from the
atoms and the O—H homolysis energies are given in Table 3.
The calculated DOH value of structure 5 differs from
the experimental energy11 by 20 kJ mol–1. Apparently,
this difference results from inaccurate procedures for deꢀ
termination of experimental values as well as from the
semiempirical PM6 approximation. At least, the calculatꢀ
ed and experimental O—H homolysis energies for 2,4,6ꢀ
triꢀtertꢀbutylphenol11,12 differ by 10 kJ mol–1. It is also
known13 that quantum chemical calculations provide reꢀ
sults varying with the procedure used.
О(1)—О(2)
О(1)—О(3)
О(2)—О(3)
О(2)—О(4)
О(3)—О(4)
14.442
13.394
13.357
—
14.151
12.782
9.613
11.332
6.829
—
The above parameters are interrelated by the formula
f = W [InH]–1
,
where InH are compounds 3—5. The chain termination
coefficient (inhibitive capacity of the antioxidant) characꢀ
terizes the number of chains that are terminated by its
single molecule. According to the data obtained, the coefꢀ
ficient f approximates to 8, 2, and 4 for compounds 5, 4,
and 3, respectively. Therefore, compound 5 as an antioxiꢀ
dant is superior to compound 4. With consideration of the
number of hydroxy groups in structures 3—5, the coeffiꢀ
cient f converted to one OH group is 2 for 3 and 5 and
smaller than unity for 4.
The O—H homolysis energy in structure 4 is substanꢀ
tially higher than those of the other compounds of the
series studied, which should affect its antioxidant properꢀ
ties. Compound 5 is the best antioxidant against heat agꢀ
ing of polymers, while compound 4 fails under these conꢀ
ditions. The dipole moment, which is a symmetry inꢀ
dicator, suggests that structure 4 is more symmetrical
( = 0.97 D) than structure 5 ( = 5.6 D).
The reaction rate constant (k7) was determined from
the equation
Structure 5 is asymmetric because its substituents are
nonequivalent compared to compound 4; this nonequivaꢀ
lence changes the O—H homolysis energy. An Xꢀray difꢀ
fraction study14 of tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydrꢀ
oxyphenyl)propanoyloxymethyl]methane has revealed the
nonequivalence of its substituents, which agrees with our
calculated data. The distances between the phenolic O
atoms, as well as the angles between the O—H bonds and
the ring C atoms, are different in structures 4 and 5 (Table 4).
The inhibition period  of cumene oxidation and the
chain termination coefficient f in reactions of the peroxyl
radical with antioxidants 3—5 at a constant initiation rate
(Wi = 1.5•10–8 mol L–1 s–1) were determined by the gasꢀ
ometric method15 (Fig. 2).
[O2]/[RH] = –k2/k7ln(1 – t –1),
where k2 = 1.75 L mol–1 s–1 (see Refs 16, 17) is the rate
constant of the ROO• initiation from cumene, [RH] =
= 7.18 mol L–1 is the concentration of cumene, and [O2]
is the amount of consumed oxygen.
[O2]•10–2/mol L–1
0.5
0.4
0.3
0.2
0.1
0
4
5
3
Table 3. PM6ꢀcalculated energies of formation of
compounds 1—5, their phenoxyl radicals, and the
O—H homolysis energies
Compound
–Ef
–EfIn•
DOH
InH
kJ mol–1
1
2
3
4
5
667.4
1287.5
1741.3
2208.3
2682.0
569.4
1186.4
1641.0
2079.0
2579.0
316.0
319.1
318.3
347.3
321.0*
20
40
60
80
100
120 /min
Fig. 2. Oxygen consumption kinetics in the initiated oxidation of
cumene at 50 C in the presence of compounds 3—5 and AIBN;
Wi = 1.5•10–8 mol L–1 s–1; [3]o = 1.34•10–5 mol L–1, [4]o
=
* For compound 5, DOH = 341 kJ mol–1 9,10
.
= 2.55•10–5 mol L–1, [5]o = 9.1•10–7 mol L–1
.

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 9, September, 2012
Volod´kin et al.
For antioxidants 3, 4, and 5, k7 is 2.5 0.2•104,
1.8 0.2•104, and 3.1 0.2•104 L mol–1 s–1, respectively.
According to the literature data, k7 is 2.3•104 (see Ref. 18)
and 1.5•104 L mol–1 s–1 (see Ref. 19) for compounds 1
and 5, respectively. It should be noted that Tsepalov et al.19
seem to have used the commercial stabilizer Irganox 1010
without analyzing its composition.
To sum up, we found that the methodology of the
preparation of tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyꢀ
phenyl)propanoyloxymethyl]methane depends on the conꢀ
ditions of methanol separation in the final step. Under the
transesterification conditions, the timeꢀdependent partiꢀ
tion of methanol in the liquid—gas system is crucial for
the reaction rates and the composition of the reaction
mixtures. The presence of compound 4 in the transesteriꢀ
fication product should be detrimental to the "consumer"
properties of the antioxidant (e.g., phenozanꢀ23).
Tris[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxyꢀ
methyl](hydroxymethyl)methane (4). A mixture of compound 1
(29.2 g, 0.1 mol), tetrakis(hydroxymethyl)methane (4.53 g,
0.033 mol), and NaOH (0.2 g, ~0.005 mol) was kept in vacuo
(1.3•104 Pa). The content of compound 4 in the reaction mixꢀ
ture was 82% (LC data). The yield of compound 4 was 22 g, m.p.
64—65 C. 1H NMR (CDCl3), : 1.43 (s, 54 H, But); 2.62 (t, 6 H,
ArCH2CH2, J = 8.63 Hz); 2.85 (t, 6 H, ArCH2CH2, J = 8.68 Hz);
3.18 (s, 2 H, CH2OH); 4.01 (s, 6 H, COOCH2); 5.09 (s, 3 H,
OH); 6.98 (s, 6 H, Ar). IR, /cm–1: 3645 (OH), 3517 br (OH),
2912 (CH), 1742 (C=O).
Tetrakis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoylꢀ
oxymethyl]methane (5). A mixture of compound 1 (116.9 g,
0.4 mol), tetrakis(hydroxymethyl)methane (13.6 g, 0.1 mol),
K2CO3 (1.5 g, ~0.01 mol), Na2CO3 (4 g, ~0.04 mol), and phenol
(4.7 g, 0.05 mol) was heated to 140—145 C and kept in vacuo
(1.3•104 Pa) for 2 h. Then the pressure was lowered to 2.6•103 Pa
and the reaction mixture was kept for 8 h, dissolved in cyclohexꢀ
ane (300 mL), and cooled to 4—5 C. The precipitate that formed
was separated. The yield of compound 5 was 61.24 g (52%), m.p.
116—117 C (cf. Ref. 7: 116—117 C). 1H NMR (CDCl3), : 1.43
(s, 72 H, But); 2.61 (t, 8 H, ArCH2CH2, J = 8.99 Hz); 2.86
(t, 8 H, ArCH2CH2, J = 7.72 Hz); 4.04 (s, 8 H, COOCH2); 5.01
(s, 4 H, OH); 6.98 (s, 8 H, Ar). IR, /cm–1: 3646 (OH), 2958
(CH), 1744 (C=O).
Experimental
1
H NMR spectra were recorded on a Bruker WMꢀ400 inꢀ
strument (400 MHz) with reference to the signals of the residual
protons of deuterated solvent (CDCl3). IR spectra were recordꢀ
ed for crystals on a PerkinꢀElmer 1725ꢀX spectrometer using the
diffuse reflection method. Liquid chromatography was carried
out on a Bruker LCꢀ31 chromatograph (IBM Cyano column,
hexane—propanꢀ2ꢀol (9 : 1) as an eluent). The chain terminaꢀ
tion coefficients f of compounds 1—5 were determined accordꢀ
ing to a known method15 for inhibited oxidation of cumene at
50 C in the presence of AIBN as an oxidation initiator. Semiemꢀ
pirical PM6 quantum chemical calculations were carried out
with the MOPAC 2009 program package. The structures of phenꢀ
oxyl radicals were calculated by the restricted Hartree—Fock
method.
Methyl 3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoate (1).
Method A. Methyl acrylate (2.5 mL, 0.03 mol) was added at
115 C to a solution of potassium 2,6ꢀdiꢀtertꢀbutylphenoxide (4.88 g,
0.01 mol) in DMSO (4 mL). The reaction mixture was cooled,
kept for 3 h, and neutralized with 10% HCl. The product was
crystallized from hexane. The yield of compound 1 was 5.16 g
(88%), m.p. 66 C (cf. Ref. 20: 66 C).
References
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Bis[3ꢀ(3,5ꢀdiꢀtertꢀbutylꢀ4ꢀhydroxyphenyl)propanoyloxymethꢀ
yl]bis(hydroxymethyl)methane (3). A mixture of compound 1
(14.6 g, 0.05 mol), tetrakis(hydroxymethyl)methane (6.8 g,
0.05 mol), and 6% KOH/aluminosilicate (3 g) as a catalyst
was kept under argon at 190 C for 40 min. Then hexane (35 mL)
was added. The lower layer containing 85% of compound 3
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graphed on silica gel. Yield 8.4 g, m.p. 105—106 C. 1H NMR
(CDCl3), : 1.43 (s, 36 H, But); 2.67 (t, 4 H, ArCH2CH2,
J = 8.21 Hz); 2.86 (t, 4 H, ArCH2CH2, J = 8.13 Hz); 3.28
(s, 4 H, CH2OH); 4.04 (s, 4 H, COOCH2); 5.01 (s, 2 H, OH);
6.98 (s, 4 H, Ar). IR, /cm–1: 3637 (OH), 3270 br (OH), 2951
(CH), 1744 (C=O).
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(in Russian).

Transesterification of 3,5ꢀBut2ꢀ4ꢀHOC6H2CH2CH2COOMe
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Received April 4, 2011;
in revised form January 23, 2012