Meng Juguang, Li Fang, Li Jian, Mo Linfeng, Tan Yiping, Xu Linshou

Guangzhou Startec Science and Technology Co., Ltd., China

Abstract A sun-screening agent isooctyl p-methoxy cinnamate was prepared by reaction of p-methoxyl benzaldehyde with isooctyl acetate using titanium tetrachloride as catalyst. The optimum conditions are as follows: molar ratio of p-methoxyl benzaldehyde to isooctyl acetate and titanium tetrachloride is 1∶1.1∶0.5; reaction temperature is 30℃; and reaction time is 6 h. The yield of isooctyl p-methoxy cinnamate can reach 98%. The method of the synthesis of isooctyl p-methoxy cinnamate is efficient and economical.

Key words sun-screening agent; isooctyl p-methoxy cinnamate; synthesis

Without taking effective protective measures,long-term exposure to ultraviolet radiation will cause different degrees of damage to skin, such as erythema,skin pigmentation, skin tumors, and skin photoaging.[1]Adopting active and effective protective measures to reduce the burden of disease caused by overexposure has become a global consensus. It is well known that the absorption wavelength of isooctylp-methoxy cinnamate is between 290～320 nm, at a high absorption rate and good solubility in lipophilic raw materials, thus easy to use and can be combined with other UVA absorbers to produce full-band UV sun-screening products. Therefore,among all suns-creenings, the most frequently used in 2007～2015 is isooctyl p-methoxy cinnamate.[2-5]

Although there have been many reports on the synthesis of isooctyl p-methoxy cinnamate,[6-10]most of them use palladium and ligand as catalyst, which is generally costly and the yield is not ideal, making many small and medium enterprises daunting. As a good shrinking agent, titanium tetrachloride has been frequently reported in recent years,[11-15]and industrial grade titanium tetrachloride is 7 yuan/kg, which is cheap and easy to obtain. The author used titanium tetrachloride to catalyze the synthesis of p-methoxybenzaldehyde and isooctyl acetate to obtain isooctyl p-methoxy cinnamate.The synthesis was a one step reaction, and the raw materials p-methoxybenzaldehyde and isooctyl acetate are cheap and easy to obtain, which greatly reduced the cost for industrial production. The synthetic reaction formula is as follows:

Experimental section

Reagents and instruments

P-methoxybenzaldehyde, isooctyl acetate, titanium tetrachloride, toluene, and sodium hydroxide are all industrial grade. Nexus-470 Fourier Transform Infrared Spectrometer, Nicolet, USA; Bruker 400 NMR spectrometer (with CDCl3as solvent, TMS as internal standard), Bruker, Switzerland; 6890 Gas Chromatograph,Agilent, USA.

Synthesis of isooctyl p-methoxy cinnamate

Add 700 g of toluene, 136 g (1 mol) p-methoxybenzaldehyde, 189 g (1.1mol) isooctyl acetate protected by nitrogen flow to a 2,000 mL three-necked flask equipped with an exhaust gas absorption device (aqueous sodium hydroxide solution, hydrogen chloride gas generated by absorption reaction), cooling slowly to 0℃, 95 g (0.5 mol)titanium tetrachloride was added dropwise about 1 h,and then heated to 30℃ for 6 h. After the reaction was completed, adjusting the pH to neutral with 2% sodium hydroxide aqueous solution, washing with water for 1～2 times, protecting the organic layer with nitrogen gas under reduced pressure and slowly heating up, firstly recovering the low boiling point solvent and impurities with water pump, then the internal temperature was 145℃ /-0.099 MPa with oil pump heat preservation distilling for 3 h to remove the unreacted raw materials and high boiling point impurities, the mother liquor was filtered, and filter cake titanium dioxide was recycled for use. The filtrate collected was isooctylp-methoxy cinnamate with clear transparent colorless to pale yellow. The yield reached 98%,and the purity of GC detection was 99.7%. IR (KBr,σ/cm-1):2,961 (m), 2,872 (m), 1,713(s), 1,607 (s), 1,578 (w),1,513 (s), 1,465 (w), 1,425 (w), 1,255 (s), 1,034 (s), 984 (w),829(s);1HNMR (400 MHz,CDCl3,δ): 7.64 (d,J=16 Hz,1H,=CH), 7.49 (d,J=8.7 Hz,2H,Ar-H), 6.90(d,J=8.7 Hz,2H,Ar-H), 6.33 (d,J=16 Hz,1H,=CH),4.17～4.07 (m,2H,-OCH2), 3.85 (s,3H,-OCH3), 1.65(q,J=5.9 Hz,1H,-CH), 1.47～1.11 (m,8H,-CH2), 0.93(q,J=7.1 Hz,6H)。

Results and discussion

The effect of titanium tetrachloride feeding mode on yield

Since titanium tetrachloride was added to the system,the temperature rose sharply. In order to prevent bumping and spraying, titanium tetrachloride should be slowly added dropwise. In the case of n(p-methoxybenzaldehyde)∶n (isooctyl acetate)∶n(titanium tetrachloride) = 1∶1.1∶ 0.5, the reaction was carried out at 30℃ for 6 h. The effect of temperature and dropping time on the yield of the target product was shown in Table 1. It can be seen from Table 1 that when the dropping temperature of titanium tetrachloride was 0℃and dropping time was 1 h, the yield reached 98% and the purity was 99.7%.

Table 1. Influence of the temperature and time of the titer on the yield of titanium tetrachloride

The effect of temperature and time on the yield

In the case of n (p-methoxybenzaldehyde): n (isooctyl acetate): n (titanium tetrachloride) = 1∶1.1∶0.5, the dropping temperature of titanium tetrachloride was 0℃,and dropping time was 1 h, the effects of temperature and time on the yield of the target product were examined,and the results were shown in Table 2. It can be seen from Table 2 that when the temperature was 30℃ and time was 6 h, the yield reached 98% and the purity was 99.7%.

Table 2. Influence of reaction time and reaction temperature on the yield

The effect of raw material ratio on yield

The titanium tetrachloride was added dropwise at 0℃for 1 h, then the reaction was continued at 30℃ for another 6 h. The effect of the ratio of raw materials on the yield was examined. The results were shown in Table 3. As can be seen from Table 3, the yield was as high as 98% when the molar ratio of p-methoxybenzaldehyden,isooctyl acetate and titanium tetrachloride was 1∶1.1∶0.5.

Table 3. Influence of the ratio of raw materials on the yield

Conclusion

The optimal condition for the synthesis of isooctyl p-methoxycinnamate using titanium tetrachloride as catalyst are as follows: n (p-methoxybenzaldehyde): n(isooctyl acetate): n (titanium tetrachloride) = 1∶1.1∶ 0.5,titanium tetrachloride was added dropwise, the dropping temperature was 0℃ and dropping time was 1 h, the reaction temperature was 30℃ and time was 6 h. The yield at this condition was 98%, and the purity tested by GC was 99.7%. This method has the advantages of low cost and easy availability, simple operation, high yield,high product purity, excellent quality and high efficiency.