SYNTHESIS OF ESTERS OF DIOXANE ALCOHOLS
951
EXPERIMENTAL
(light yellow mass) was a mixture of esters of adipic
acid and dioxane alcohols, with an admixture of di-
butyl adipate and zinc stearate. The product yield was
97% of the theoretical value; the content of the mix-
ture of the esters was no less than 98%.
Esters of dioxane alcohols were prepared by two
procedures.
(1) Carboxylic acids (acetic, adipic, phthalic,
butyric, oxalic) were esterified with dioxane alcohols
in the presence of acid catalysts (sulfuric, phospho-
ric, benzenesulfonic acids; KU-23 cation exchanger).
The reactions were performed at 140 165 C for 4
6 h in an excess of dioxane alcohols (molar ratio 4 :1).
The acid conversion did not exceed 30%; the reaction
mixture was dark.
The qualitative analysis of the product was per-
formed by GC/MS on a Finnigan Trace DSQ device
in the chemical ionization (isobutane) mode (in the
electron impact mode, the molecular ions were not
recorded). For the major components, we obtained
m/z 331 and 403 ([M + H]+), which corresponds to
the molar weights of the following compounds:
(2) It was suggested to prepare esters of dioxane
alcohols by ester interchange catalyzed by both acid
and base catalysts, and also by transition metal salts
[14].
CH3
CO O CH2CH2
CO O CH2CH2
O
CH2
O
C
CH2 CH2
(CH2)4
The latter procedure involved two steps: esterifica-
tion of adipic acid with butanol to obtain dibutyl adi-
pate and ester interchange of dibutyl adipate with
dioxane alcohols.
CH2 CH2
O
C
CH3
O
CH2
1
M = 402 g mol
Esterification of adipic acid was performed with
an excess butanol; concentrated sulfuric acid was used
as a catalyst. The temperature was maintained within
90 117 C, which enabled distillation of the azeotrope.
The concentration of adipic acid in the reaction mix-
ture was monitored titrimetrically [15].
CO O C4H9
(CH2)4
CH2 CH2
O
CO O CH2CH2
C
CH3
O
CH2
1
M = 330 g mol
The reaction was stopped at a 98% conversion of
adipic acid. Then the mixture was cooled and washed
to neutral reaction. Water and excess alcohol were
removed from the resulting crude ester by distillation
at atmospheric pressure. The ester was distilled at
15 mm Hg; the fraction boiling at 210 213 C was
collected. The dibutyl adipate obtained was analyzed
for the acid number by the standard procedure [18].
The acid number of dibutyl adipate should not exceed
Thus, ester interchange of dibutyl adipate with
dioxane alcohols yields a mixture of isomeric mono-
and disubstituted esters.
To evaluate the plasticizing power of the product,
we prepared samples of the middle PVC layer of cal-
ender-rolled linoleum. The samples had the following
composition (%): PVC 51, chalk 21, dioctyl phthalate
13, test plasticizer 13, and calcium stearate 2.
1
0.05 (mg KOH) g . A higher acid number results in
darkening of the reaction mixture in the step of ester
interchange of dibutyl adipate with dioxane alcohols.
As the lower layer we used cotton underwarp
(Netkol). A PVC film with a printed pattern is applied
onto the upper layer; all the three layers are doubled
on a Bersdorf continuous press.
The ester interchange of dibutyl adipate was per-
formed in an excess of dioxane alcohols in the temper-
ature range 215 250 C, so as to ensure continuous
distillation of the released butanol at a vapor temper-
ature of 117 120 C. The released butanol can be re-
turned to the step of esterification of adipic acid.
As catalyst we used zinc stearate.
The plastic compound was prepared from a suspen-
sion PVC, special stabilizers and pigments, and the
test plasticizer (35 40 wt % of the total).
Our experiments showed that esters of dioxane
alcohols could not be prepared in reasonable yields
and with acceptable quality by esterification with
carboxylic acid. Even weak acid catalysts, such as
cation exchangers, caused dehydration of dioxane
alcohols with ring opening and formation of triols
and unsaturated compounds:
The completeness of the ester interchange was
judged from the amount of the butanol released. The
reaction was stopped at a 85 90% conversion of di-
butyl adipate.
From the reaction mixture, we distilled off low-
boiling components; the remaining target product
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005