The EOLC had been analyzed by several researchers (Ye, 1992; Cheng, 1995; Liu et al., 2001; Wang et al., 2002) . Recently, it reported that the essential oil of Litsea cubeba contained 29 compounds (see Table 1) (Hu et al., 2011), which mainly contains terpenes, lipids and fatty acids. On account of one of the double bonds binding with four different groups, citral has two geometric isomers, which are the E isomer (geranial) and the Z isomer (neral) (Scheme 1). The content of citral in EOLC was as high as 70%. The content of limonene was 10% and the content of other components was 20% approximately (Table 1). The experiments details as follows:

Geranyl nitrile with lemony-fresh odor similar to citral (Calkin and Jellinek, 1994) is widely used as fragrance

Scheme 1. The two geometric isomers of citral.

ingredients and incorporated into a variety of consumer product types, including soaps, shampoos, cosmetics, perfumes, detergents and insect repellents (Potter et al., 2001; Arctander, 1969). The geranyl nitrile is appre-

^aRetention Index; ^bIndentified by good match of mass spectrometer; ^cIdentified by retention index and compared with those reported in the literature (Qin, 2008) ; dIdentified by retention time of standard compounds.

ciated for its comparative stability under mildly alkaline conditions, which makes it particularly suitable to applications in soaps, detergents.

Zheng reported citral directly reacting with ammonia in the presence of active copper and molecular sieve as catalyst. The yield could reach 90% (Scheme 2). However the reaction demonstrated some disadvantages: Firstly, the reaction endured so high temperature that the reaction led to more energy consuming; Secondly, this reaction had many side reactions, thus the product was difficult for purification. In 2001, Nong adopted tetrabutylammonium bromide as transfer phase catalyst, and acetic anhydride as dehydrant in mild condition to synthesis of geranyl nitrile; and the yield was 91% (Nong et al., 2001) . Zhou carried out the reaction with hydroxyl amine sulftrate. This procedure was more facile and convenient. And yields were good to excellent. However, excess amount of citral was employed (Zhou et al., 2005) .

Pseudoionone is a key intermediate for preparation of ionone. Usually, pseudoionoine is applied in fragrance, food additives and perfume field (Rajuet et al., 2011) .

Pseudoionone is prepared by citral condensing with acetone in the presence of catalysts (Scheme 3) basically.

Scheme 2. Synthesis of geranyl nitrile with ammonia.

Scheme 3. Preparation of pseudoionone using citral and acetone as starting materials.

This reaction is simple and facile to carry out. Researchers were focusing on exploring the catalysts. Zhou reported the aldol condensation between citral and acetone. The reaction was performed by using catalytic amount of sodium hydroxide or potassium hydroxide (2%) in the presence of 6 equivalents of acetone; moderate to good yields were obtained (Zhou et al., 2009) . Catalyst was crucial for the reactions, and many catalysts were screened and modified for improving the reactions, such as: EtONa/EtOH (Wang, 1990) , KOH/MeOH (Wang and Jiang, 1993) and so on. The yields of the reactions could get 86%, and purity could get 97%. However, there were still many side reactions such as citral self-condensation, acetone self-condensation and so on occurring in the reaction.

Methyl ionone known as high-grade fragrance with fresh odor is mainly used in fragrance and food additives. In 1980, Guo described the synthesis of methyl ionone use KOH and methanol as condensation agent, and the yield was 89%. Meanwhile, using phosphoric acid as cyclization agent, and the yield was 70% (Guo et al., 1980) . In 2002, Lin investigated macroreticular resin as catalysts for cyclization of the pseudomethylionone to produce methylionone (Lin and Liang, 2002; Tang, 2011) . The methyl ionone could be prepared by aldol condensation and ring-closed reaction (Scheme 4). The typical procedures were as follows: methyl acetone in 250 ml flask added 5% NaOH 30 ml with stirring, then dropped EOLC at 35˚C - 40˚C for a few hours in the presence of catalysts. In 2003, Huang reported that citral and 2-butyl acetone as starting materials in the presence of quaternary ammonium hydroxide and solid super acid TiO₂/SO₄²⁻ as catalyst. Yields were 90% - 92%. However, the dimethyl benzene as solvent was difficult to remove off from the products. In 2004, Lin developed a new method: the anion exchange resin as catalyst, the yield was quantitative, but the large amount of catalyst was consumed (Lin 2004) .

β-ionone, an important contributor to fragrance in many flowers (Kaiser and Lamparsky, 1980; Cooperet et al., 2003) , is an abundant source of useful aroma compounds existing in a variety of essential oils with various application in fragrance, perfume industry. In addition, β-ionone is key intermediate to prepare vitamin E, vitamin A and extensively used in cosmetics (Kanei et al., 1999) , food flavor and inhibitor (Yu et al., 1995; Plotto et al., 2006) .

Citral condensing with acetone under base condition is the typical method of synthesis of β-ionone, then through ring-closure reaction forming β-ionone in the presence of catalyst (Scheme 5) (Hertel et al., 1986). During the whole reaction, selecting the excellent catalyst is vital for the whole reactions. Hence, many researchers had been working on the selecting and applying catalysts such as sodium hydride, KF/Al₂O₃, LiOH (Lu and Yao, 2007; Zhang et al., 2010) , phosphoric acid. Transfer phase catalyst Bu4N⁺Br⁻, Et₃N⁺CH₂PHCl⁻ (Liu et al., 2000) . The yields varied from mediate to good.

Scheme 4. Synthesis of Methyl ionone.

Scheme 5. Typical method of synthesis of β-ionone.

Vitamin A is a group of unsaturated nutritional organic compounds, which includes retinol, retinal, retinoic acid, and several provitamin A carotenoids (Damodaran and Parkin, 2008) . Vitamin A is a vital medicine, which is widely used for nyctalopia, eye and skin dryness. It is important for growth and development for the maintenance of the immune system and vision (Tanumihardjo, 2011) .

Vitamin A was first synthesized in 1947 by two Dutch chemists. Then, scientists and industry managed to commercialize Vitamin A (Robeson et al., 1955) . Vitamin A has a special structure: β-ionone ring to which an isoprenoid chain attached. In 1947, the Roche Company commercialized the product using beta-ionone as starting materials through Dazens reaction, Grignard reaction, hydrogenation acetylation, bromination, elimination (Scheme 6). However, 50 more reagents were employed and many reaction units were employed. Years later, BASF Company invented a new route that beta-ionone as starting materials underwent ethynylation, reduction and elimination. This synthetic pathway was simple and economical. Meanwhile the yield was high. However, the drawbacks were secondary key intermediates C₅ aldehyde difficult to synthesizing.

Vitamin E is the most important industrial fat-soluble antioxidant, which includes tocopherols and tocotrienols,

Scheme 6. Synthesis of Vitamin A.

extensively applied as antioxidant, anti-cancer drugs, free radical scavenger (Bowry et al., 1995) . Vitamin E could improve human physical immunity, and used as animal feeds (Bonrath et al., 2007) .

Vitamin E, generally, is synthesized by two building blocks through the Friedel-Crafts alkylation reaction. One building block is 2,3,5-trimethyl hydroquinone (TMHQ), and the other building block is isophytol (Scheme 7). And the mechanism of the reaction is enol under the catalyst of AlCl₃ forming carbocations binding with TMHQ. To date, there are only four companies producing Vitamin E in large scale. Isophytol is a key material for the synthesis of vitamin E. Usually, isophytol was synthesized by using citral or pseudoionone as starting materials, through serials of reactions (Sato et al., 1963) . And the study to date was focused on catalyst selecting and modification. Many solid acids were applied to replace the liquid acid. Qian used phosphomolybdic acid as catalyst obtained good yield. The purity could get 88% (Qian et al., 1999) . Makoto employed scandium (Ⅲ) trifluoromethanesulfonate as an efficient catalyst (Matsui et al., 1995) . Bulychev employed amine as catalyst (Bulychev and Kartsev, 1999) .

The citral could condensation with amines and amino acids. Saddiq used citral reacted with cytosine, this product showed the good antibacterial and antifungal activity, especially on staphylococcus aureus (Saddiq and Khayyat, 2010) . And the synthesis route as follow (scheme 8).

Chitosan, a biocompatible, biodegradable, non-toxic polymer, is prepared from chitin, which is the second most naturally occurring biopolymer after cellulose. The Schiff base of chitosan was synthesized by the reaction of chitosan with citral under high-intensity ultrasound (Scheme 9). The effect of the molar ratio of chitosan to citral, reaction time, and temperature on the yield has been investigated. The optimal conditions were a temperature of 50˚C, a molar ratio of chitosan to citral of 1:6, and a reaction time of 10 h. The maximum yield achieved was 86.4% under optimum conditions. The structure of the schiff base was characterized by FTIR spectroscopy, elemental analysis, and X-ray diffraction studies. The strong peaks at 1648.3 and 1610.6 cm⁻¹ are due to C-N bond and C-C bond stretching vibrations. The results confirmed that amino groups on chitosan reacted with citral to form the Schiff base. The antimicrobial activities of chitosan and Schiff base of chitosan were investigated against Escherichia coli, Staphylococcus aureus, and Aspergillus niger. The results indicate that the antimicrobial activity of the Schiff base increases with an increase in the concentration. It was also found that the

Scheme 7. Synthesis of Vitamin E.

Scheme 8. Synthesis of nitrogen derivatives with nitral as starting materials.

Scheme 9. Synthesis of chitosan derivatives.

antimicrobial activity of the Schiff base was stronger than that of chitosan (Jin, 2009) .