Esters of diphenic acid and their plasticizing properties
Abstract Generated abstract
This study examines esters of diphenic acid as potential plasticizers for polyvinyl chloride, motivated by the practical use of related dibasic acid esters. Diisoamyl diphenate, di-2-ethylhexyl diphenate, and a mixture of heptyl, octyl, and nonyl diphenates were synthesized by esterification of diphenic acid with the corresponding alcohols, and their physicochemical properties, ultraviolet absorption, electrical resistivity, and behavior in PVC compositions were measured. The resulting esters were viscous oily liquids with properties comparable in several respects to established plasticizers such as dioctyl phthalate and dioctyl sebacate. PVC plasticates prepared with the new esters showed favorable thermal stability, low heating losses, nonflammability after flame removal, and technical characteristics that the authors judged not inferior to those obtained with known plasticizers.
Full Text
Esters of Diphenic Acid and Their Plasticizing Properties
L. P. Kulev, R. N. Gireva, A. M. Ittenberg, E. S. Belostudneva
Among the derivatives of diphenic acid, esters are undoubtedly of practical interest; like the esters of phthalic and other dibasic acids, they may find application as plasticizers for polymeric materials (polyvinyl chloride, polystyrene resins, cellulose esters, and others).
The literature describes acid and neutral esters of diphenic acid with the alcohols methyl [1, 2, 3, 4, 6], ethyl [1, 5, 6], n- [6, 7] and isopropyl [7], n-butyl [6, 7, 8], n-hexyl [7], n-decyl [6], and 2-ethylhexyl [8]. The indicated esters were obtained from diphenic acid or its anhydride and the corresponding alcohols. Dibenzyl ester [7] was obtained by the interaction of the disodium salt of diphenic acid with benzyl chloride in the presence of triethylamine. Beginning with the propyl esters, these esters may serve as plasticizers for nitroxylin, polyvinyl chloride, and others [7].
The aim of our work was to obtain certain esters of diphenic acid of the general formula
\[ \mathrm{AlkOOC} \begin{matrix} \text{diphenyl nucleus} \end{matrix} \mathrm{COOAlk} \]
and to test them as plasticizers for polyvinyl chloride resin.
By the methods described below, the following esters of diphenic acid were obtained: diisoamyl, di-2-ethylhexyl (diisooctyl), and a mixture of esters of diphenic acid with higher fatty alcohols \((C_7—C_9)\). The latter are products of hydrogenation
Fig. 1. Absorption spectra of esters of diphenic acid in ethyl alcohol \((10^{-4}\ \mathrm{mol}/l)\). 1 — diisoamyl diphenate, 2 — di-2-ethylhexyl diphenate, 3 — mixture of diheptyl, dioctyl, and dinonyl diphenates.
higher fatty acids obtained in the oxidation of paraffin hydrocarbons and not finding industrial application.
All the esters are oily liquids of light-yellow or light-brown color, which do not distill without decomposition at ordinary pressure.
Figure 1 shows the absorption curves of these esters in the ultraviolet.
The measurements were carried out in ethyl alcohol on an SF-4 spectrophotometer.
The plasticizing properties of the esters were tested at the Novosibirsk Chemical Plant.
Experimental Part
Diisoamyl ester of diphenic acid (I). In a flask with a reflux condenser and a trap for collecting water, a mixture of 10 g of diphenic acid, 22 ml of isoamyl alcohol (threefold amount), and 1 ml of sulfuric acid (sp. gr. 1.84) is boiled for 4–5 hours, until water ceases to separate. The mixture is treated with a 5% solution of soda, washed with water to a neutral reaction, and dried with calcium chloride. The excess isoamyl alcohol is removed under vacuum while heating on a water bath, and the ester obtained is distilled at 279–280° (4 mm).
Diisoamyl ester of diphenic acid is a light-yellow viscous oil; \(d_{4}^{20} = 1.0498\), \(n_{D}^{20} = 1.529\). Yield of ester 12.6–13.4 g (80–85%).
Di-2-ethylhexyl ester of diphenic acid (II). In a three-necked flask equipped with a reflux condenser with a trap for collecting water, a stirrer, and a thermometer, 60.5 g (0.25 M) of diphenic acid, 162.5 g (1.25 M) of 2-ethylhexyl alcohol, and 1.2 g of 4-toluenesulfonic acid (2% of the weight of diphenic acid) are heated (\(t^\circ\) 128–145) under vacuum (115–130 mm) for 12 hours. At 4 and 7 hours after the start of the reaction, a further 0.6 g of 4-toluenesulfonic acid is added to the mixture each time. Heating is continued until the theoretical amount of water (9 ml) has separated and the acid number of the reaction mixture has decreased to 2.41. The mixture is neutralized with a twofold amount (76 g) of a 1% sodium hydroxide solution with heating (75–85°) and constant stirring for 2.5 hours, to an acid number equal to 0.173 mg KOH. It is washed repeatedly with water to a neutral reaction. The excess 2-ethylhexyl alcohol is distilled off from the ester under vacuum (6–9 mm). The ester, cooled to 30–40°, is filtered from a small amount of solid impurities. Yield of ester 104.8 g (89.95%). The specific electrical volume resistivity of the ester is \(1.65 \cdot 10^{10}\ \Omega \cdot \text{cm}\).
For purification, the ester is heated with charcoal and gumbrin for 1 hour at 80–85° and filtered twice. The ester is a viscous brown liquid, distilling with partial decomposition at 288–289° (4 mm). After distillation the color of the ester becomes yellow.
Mixture of heptyl, octyl, and nonyl esters of diphenic acid (III). Obtained analogously to (II) from 60.5 g of diphenic acid, 162.5 g of higher alcohols of the \(C_7—C_9\) group, and 0.605 g (1% of the weight of diphenic acid) of concentrated sulfuric acid (sp. gr. 1.84) with heating to 120–130° under reduced pressure (115–175 mm). Three hours after the start of the reaction, a further 0.3 g of concentrated sulfuric acid is added to the mixture. Esterification is continued for 10 hours to an acid number close to the theoretical value (2.3 mg KOH). The mixture is neutralized with a twofold amount (77.3 g) of a 1% sodium hydroxide solution while heating to 80° and stirr—
heating for 2 hours to an acid number equal to 0.227 mg KOH. It is washed repeatedly with water to a neutral reaction, and the excess alcohol is distilled off under vacuum (6 mm). It is cooled to 30–40° and filtered. The yield of the ester mixture is 110.6 g (95.04%). The specific electrical resistance of the ester mixture is \(1.426 \cdot 10^{10}\) ohm·cm. The esters are purified by heating with charcoal and bleaching earth to 85–90° for 1 hour and filtered twice. The esters are a rather viscous dark-brown liquid, distilling with partial decomposition at 280–290° (4 mm). The distilled esters are a light-brown liquid.
The principal physicochemical characteristics of the esters obtained and of several known plasticizers are given in Table 1.
Table 1
| No. | Name of indices | Di-2-ethylhexyl diphenate | Mixture of dihexyl, dioctyl, and dinonyl diphenates | Dioctyl phthalate | Dioctyl sebacate |
|---|---|---|---|---|---|
| 1 | Specific gravity \((d_4^{20})\) | 1.0115 | 1.0147 | 0.982 | 0.913 |
| 2 | Acid number (in mg KOH per 1 g of ester) | 0.29; 0.22 | 0.45–0.25 | 0.2 | 0.3 |
| 3 | Saponification number (in mg KOH per 1 g of ester) | 230–231 | 224–226 | 282–292 | 260–270 |
| 4 | Molecular weight | Found 477; Calculated 466 | Found 498; Calculated 456 | -- | -- |
| 5 | Content of volatile substances, % | 0.37 | 0.28 | 0.2 | 0.3 |
| 6 | Viscosity \((\eta)\), in cP | 288 | 87.6 | -- | -- |
| 7 | Specific electrical resistance \((\rho)\), in ohm·cm | \(5.067 \cdot 10^{10}\) | \(2.479 \cdot 10^{10}\) | \(2 \cdot 10^{10}\) | \(3 \cdot 10^{10}\) |
| 8 | Boiling temperature, °C (4 mm) | 288–289 | 280–290 | — | — |
| 9 | Refractive index \((n_D^{20})\) | 1.521 | 1.520 | — | — |
It is evident from the table that the esters obtained, in a number of properties, merit attention as good plasticizers.
Preparation of vinyl chloride plastics with esters of diphenic acid. The plasticizer composition is prepared from PF-grade chlorinated resin according to the formulation:
| Component | Amount |
|---|---|
| special PF resin | 100 parts by weight |
| plasticizer | 45 parts by weight |
| lead silicate (stabilizer) | 12 parts by weight |
| calcium stearate | 3 parts by weight |
Lead silicate is ground in a mortar with a small amount of plasticizer, calcium stearate is added and the mixture is ground again; the remaining plasticizer and resin are added. Everything is thoroughly mixed—
[[unclear: beginning of sentence]] until a homogeneous mass is obtained. For “maturation” and swelling of the composition, it is heated for 1.5 hours in a water bath to 80–85° with constant stirring and then left to stand for 10–15 hours. From each type of plasticate, samples 1 mm and 0.5 mm thick are rolled out.
The technical characteristics of the plasticates obtained and of the standard plasticates are given in Table 2.
Table 2
| No. | Name of indicator | Unplasticized polyvinyl chloride | Hose plasticate according to VTU MKhP 1585-47 | Insulation plasticate I according to VTU MKhP 1585-47 | Insulation plasticate II according to VTU MKhP 1585-47 | Plasticate with di-2-ethylhexyl ester of diphenic acid | Plasticate with a mixture of diheptyl, dioctyl, and dinonyl esters of diphenic acid |
|---|---|---|---|---|---|---|---|
| 1 | Specific volume resistivity \((\rho)\) at 20°C, in ohm·cm | up to \(1 \cdot 10^{10}\) | \(1 \cdot 10^{9}\) | \(1 \cdot 10^{13}\) | \(1 \cdot 10^{14}\) | \(4.2 \cdot 10^{11}\) | \(4.1 \cdot 10^{11}\) |
| 2 | Decomposition temperature, not lower than °C | 180–210 | 200 | 200 | 200 | 221 | 219 |
| 3 | Tensile strength, in kg/cm | 500–600 | 140 | 180 | 190 | 232 | 21 |
| 4 | Elongation, in % | 10–20 | 280 | 200 | 180 | 197 | 200 |
| 5 | Losses on heating, not more than % | — | 3 | 3 | 3 | 0.77 | 0.84 |
| 6 | Flammability | Does not burn when removed from the flame | Does not burn when removed from the flame | Does not burn when removed from the flame | Does not burn when removed from the flame | Does not burn when removed from the flame | Does not burn when removed from the flame |
Thus, plasticates with esters of diphenic acid, in their most important technical properties, are not inferior to plasticates obtained with known plasticizers.
Conclusions
- Esters of diphenic acid have been obtained: diisoamyl, di-2-ethylhexyl (diisooctyl), and a mixture of esters of higher fatty alcohols (heptyl, octyl, and nonyl), and their properties have been studied. Testing these esters as plasticizers for polyvinyl chloride resin gave good results.
Literature
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