An efficient and facile procedure for synthesis of octyl

polyglucoside

Ying Wu, Jiu Gao Yu *, Xiao Fei Ma, Jian She Zhang

Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China

Received 31 May 2007

Abstract

Nonionic surfactant alkyl polyglucoside (APG) was prepared by direct glycosidation of alkyl alcohol with glucose in the

presence of sulfate acid–silica gel (H2SO4/SiO2) as solid acidic catalyst. The quantity of catalyst was only of 1 wt%, based on the

glucose, and the conversion of glucose was close to 100% at 110 8C in 1.5 h. The product was characterized by FT-IR, mass and 1H

NMR spectra. The degree of polymerization (DP) of the glucose in the product was 1.37, and critical micelle concentration (CMC)

of product was only 0.0104 wt%.

# 2007 Jin Gao Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Alkyl polyglucoside; Sulfate acid–silica gel; Solid acidic; Catalyst

Alkyl polyglycosides (APGs) are widely used as nonionic surfactants in cosmetic, biology, medicine [1,2],

agriculture and kitchen detergency [3,4] due to their good dermal tolerance, low toxicity, environmental compatibility

[5] and outstanding physical properties [6]. They are synthesized from renewable and abundant natural materials [7]

such as fatty alcohols and carbohydrates. With good catalytic activity, H2SO4 is widely used for synthesis of APGs in

tradition. But as a liquid acid, H2SO4 cannot be separated from materials and products easily and erodes the

equipment. Sato et al. [8] indicate that SiO2 is the best carrier of H2SO4 which can keep its activity and long catalyst

life for the nitration of benzene. In this paper, H2SO4/SiO2 gel as solid acidic catalyst is used which avoids the

disadvantage of liquid H2SO4 and keeps at a mild reaction conditions. Active centers of H2SO4/SiO2 are homogeneous

and the acidity of it is similar to liquid H2SO4.

20.8 g tetraethoxysilane, 14.4 g deionized water and 2.2 mL hydrochloric acid (0.04 mol/L) were introduced in a

250 mL three necked, round bottom flask equipped with a mechanical stirrer. The mixture was stirred at room

temperature to form hyaloid collosol. 8.8 mL sulfuric acid aqueous solution (1:1 v/v) was added into the collosol with

strong stirring, and the gel of H2SO4/SiO2 was formed gradually. After aging for 2 h, the gel was heated at 110 8C for

2 h and ground into powder (mesh 100), then kept in a desiccator over P2O5 for further use [9]. The content of sulfuric

acid in catalyst was 5.78 mmol/g.

According to the synthetic route shown in Scheme 1, 666 mmol of octanol was placed in a 250 mL three necked,

round bottom flask equipped with a mechanical stirrer, a thermometer and a cooled reflux condensor. With stirring,

20.0 g of anhydrous glucose (111 mmol) was introduced into the flask and dispersed adequately in 10 min. Then the

www.elsevier.com/locate/cclet

Chinese Chemical Letters 18 (2007) 1173–1175

* Corresponding author.

E-mail address: wyamengster@gmail.com (J.G. Yu).

1001-8417/$ – see front matter # 2007 Jin Gao Yu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2007.07.023

mixture was heated and kept the reaction temperature at 110 8C. The reaction was started by adding 0.2 g of H2SO4/

SiO2. At the same time, pressure in the reaction system was reduced to 20 mbar so that the formed water could be

removed in time. Otherwise, the presence of water not only motivated the hydrolysis of product, but also dissolved and

caramelized glucose. After 1.5 h, the reaction was terminated by cooling to ambient temperature. H2SO4/SiO2 and

remaining glucose were filtered from the organic phase, and then separated by solid–liquid extraction in a soxhlet

using 70% ethanol.

According to the synthetic route shown in Scheme 1, 666 mmol of octanol was placed in a 250 mL three necked,

round bottom flask equipped with a mechanical stirrer, a thermometer and a cooled reflux condensor. With stirring,

20.0 g of anhydrous glucose (111 mmol) was introduced into the flask and dispersed adequately in 10 min. Then the

mixture was heated and kept the reaction temperature at 110 8C. The reaction was started by adding 0.2 g of H2SO4/

SiO2. At the same time, pressure in the reaction system was reduced to 20 mbar so that the formed water could be

removed in time. Otherwise, the presence of water not only motivated the hydrolysis of product, but also dissolved and

caramelized glucose. After 1.5 h, the reaction was terminated by cooling to ambient temperature. H2SO4/SiO2 and

remaining glucose were filtered from the organic phase, and then separated by solid–liquid extraction in a soxhlet

using 70% ethanol solution. The product, octyl polyglucoside (OPG), in organic phase was obtained by evaporation in

vacuum. The conversion of glucose was nearly 100%.

Data of OPG were shown here.

OPG: FT-IR (KBr) max: 3300–3400, 2920, 2860, 1460, 1250, 1060, 720, 650–400 cm�1; m/z: 315.3 [C8G1 + Na]+,

m/z 477.3 [C8G2 + Na]+ m/z 639.4 [C8G3 + Na]+; 1H NMR (D2O 500 MHz, dppm): 0.719 (t, 3H, –CH3), 1.150 (m, 10H,

5� –CH2–), 1.485 (m, 2H, –CH2–), 3.0–4.3 (m, CH–O and –CH2–O).

Along with the synthesis of APG, the polymerization of glucose was unavoidable. The value of DP was estimated

from the 1H NMR spectra by formula (1). The peaks of CH3(CH2)5CH2– located in the region of 0.0–1.6 ppm. The

integral of this area was 8.83 (R

Ha) and the total hydrogen number was 15. So the integral of one hydrogen was 0.5887

(R

Ha=15). Peaks of sugar groups and –CH2– joined to the sugar groups (2H) distributed from 3.0 to 4.3 ppm, where

the total integral area was 6.83 (R

Hb). So the integral of hydrogens on sugar groups was 5.6526 (R

Hb � 0:5887� 2).

It indicated that the number of hydrogens on sugar groups was 9.6018 (5.6526/0.5887). It should be seven hydrogens

on one glucose group theoretically, so there were 1.37 (9.6018/7) glucose rings on sugar groups. That was to say, DP of

the sample was 1.37.

DP ¼

�RHb � 2

15=R

Ha

�=

�RHa

15

�

7(1)

The solid catalyst was easily regenerated by filtering from the reaction mixture, and drying at 110 8C for 2 h. The

catalyst could be reused times for the synthesis of APG without significant loss of activity. The results are summarized

in Table 1.

As demonstrated by measuring the surface tension of aqueous solutions with different concentrations (Fig. 1), OPG

showed 30.34 mN/m at 25 8C. The corresponding CMC was only 0.0104 wt%.

In conclusion, we have described a mild, highly efficient and reusable catalyst for the preparation of APGs by direct

glycosidation. In addition, the procedure offers several advantages including high conversion, low value of DP, low

CMC, and minimal environmental impact, which make it a useful and attractive process for the synthesis of APGs.

Y. Wu et al. / Chinese Chemical Letters 18 (2007) 1173–11751174

Scheme 1.

References

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23.

[4] D. Balzer, H. Luders, Nonionic Surfactants: Alkyl Polyglucosides (Surf. Sci. Ser.), vol. 91, 1st ed., Dekker, New York, 2000, p. 335.

[5] P. Schoberl, W. Guhl, N. Scholz, K. Taeger, Tenside Surfact. Detergents 35 (4) (1998) 279.

[6] L. Zhang, P. Somasundaran, C. Maltesh, Langmuir 12 (10) (1996) 2371.

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Y. Wu et al. / Chinese Chemical Letters 18 (2007) 1173–1175 1175

Table 1

Reuses of the catalyst for syntheses of OPG

Entry Conversion (%)

1 100

2 100

3 99

4 98

5 98

6 95

Fig. 1. Surface tension of OPG.