Synthetic strategy of cyclopentadecanone and cyclopentadecanolide
Although there are many preparation methods for cyclopentadecanone [14, 15], the key reaction step is shown in Fig. 1.
Therefore, the most important difficulty in the synthesis of cyclopentanone is how to obtain raw material MeOOC(CH2)13COOMe or HOOC(CH2)13COOH. Cyclopentadecanolide and cyclopentadecanone have similar carbon structure. Its commercial synthesis method is based on 15-hydroxypentadecarboxylic acid [4, 5]. Guo et al. [25] prepared 15-pentahydroxypentadecanoic acid from Malania oleifera Chum oil, and synthesized cyclopentadecanolide. The synthetic route is shown in Fig. 2.
Although on chemical synthesis, the preparation of mixed fats of is simple from Malania oleifera Chum oil, but separation of 15-tetracosenic acid is difficult to use crystallization method, because15-tetracosenic acid, 9-octadecenoic acid and erucic acid properties are similar in mixed fats. The yield of 15-tetracosenic acid (purity 95%) is only about 10% from Malania oleifera Chum oil.
In order to make efficient use of Malania oleifera Chum oil (1) resources and shorten the synthesis route of cyclopentadecanone (2) and cyclopentadecanolide (3), we proposed a synthesis strategy, as shown in Fig. 3.
Preparation of cyclopentadecanone
Firstly, we conducted a typical synthesis method experiment, and the synthesis route is shown in Fig. 4.
Since the yield of 15-tetracosenic acid with a purity of more than 90% obtained from Malania oleifera Chum oil is low, the yield of cyclopentadecanone is only 12.8%.
Then, we carried out the synthesis experiment according to the synthesis strategy (Fig. 3). It is noteworthy that in Fig. 3, when group Me is replaced by other groups, does it affect the yield? The effect of groups on the yield of cyclopentadecanone was investigated and the result was shown in Table 1.
Table 1
the effect of groups on the yield
Ester groups
|
Yields* of cyclopentadecanone (%)
|
methyl
|
32.7
|
ethyl
|
38.5
|
propyl
|
31.1
|
butyl
|
21.0
|
typical synthetic route
|
12.8
|
*in terms of 15-tetracosenic acid |
Table 1 show that the yield of cyclopentadecanone from ethyl ester was the highest (38.5%) among these ester groups. If it is compared with the typical synthetic route, the yield of the new synthetic strategy is about three times that of the typical synthetic route. Therefore, when cyclopentadecanone is synthesized according to the synthesis strategy, the utilization rate of nerve acid in Malania oleifera Chum oil is high.
Comparing the prepared cyclopentadecanone with the standard cyclopentadecanone, IR (KBr), GC-MS, 1H NMR (600 MHz, CDCl3) and 13C NMR (600 MHz, CDCl3) are identical.
Cyclopentadecanone is white solid, m.p. 60 ~ 61 ℃. IR (KBr): 3411, 2928, 2855, 1710, 1459, 1445, 1408, 1286, 1211, 1126, 720 cm− 1. 1H NMR (600 MHz, CDCl3): δ = 2.414−2.392 (4 H, s), 1.642−1.620 (4 H, s), 1.289 (20 H, s). 13C NMR (600 MHz, CDCl3): δ = 212.99, 42.23, 27.69, 26.89, 26.83, 26.54, 26.39, 23.58. GC-MS (EI): m/z = 224.4 (M+).
Preparation of cyclopentadecanolide
Malania oleifera Chum is a renewable plant resource, and using its oil to synthesize cyclopentadecanolide has good application value.When cyclopentadecanolide was synthesized according to the preparation method of Fig. 2, its total yield was only 15.3%, and active ingredient utilization rate is low.
In order to make efficient use of resources, we designed a synthesis strategy, in the synthesis strategy (Fig. 3), alkali catalyst is very important, so the catalyst effect was investigated, and the result was shown in Table 2.
Table 2
Effect of catalysts on yields of cyclization
catalysts on
|
Yields of cyclopentadecanolide (%)*
|
NaOH
|
37.0
|
CH3ONa
|
52.0
|
CH3ONa/ NaOH
|
63.0
|
preparation method of Fig. 2
|
15.3
|
*in terms of 15-tetracosenic acid |
Table 2 shows that the yield of cyclopentadecanolide is 63% when using mixed catalyst CH3ONa/ NaOH, it is high compared with catalyst single NaOH or CH3ONa. Compared with the synthesis route in Fig. 2, the yield of the new synthesis strategy is 4.1 times that of the synthesis method in Fig. 2. Therefore this synthesis strategy is short and has the value of industrial application.
Comparing the prepared cyclopentadecanolide with the standard cyclopentadecanolide, IR (KBr), GC-MS, 1H NMR (600 MHz, CDCl3) and 13C NMR (600 MHz, CDCl3) are identical.
Cyclopentadecanolide is white solid, m.p. 36 ~ 37 ℃. IR (KBr): 3445, 2685, 1636, 1630, 1448, 1370, 1350, 1285, 1236, 1109, 1071, 1065, 1015, 723 cm− 1. 1H NMR (600 MHz, CDCl3): δ = 4.138, 2.331, 1.641, 1.422, 1.323. 13C NMR (600 MHz, CDCl3), δ = 173.97, 63.99, 34.45, 28.46, 27.82, 27.18, 26.99, 26.76, 26.45, 26.15, 26.04, 25.98, 25.18, 24.96; GC-MS (EI): m/z = 240.2 (M+).