Читать книгу High-Performance Materials from Bio-based Feedstocks - Группа авторов - Страница 65

Starbon‐400‐SO₃H has been used to form amides in excellent yields from a range of anilines and acetic acid under microwave irradiation [27].

After 15 minutes, at a maximum temperature of 130 °C, yields approaching quantitative were achieved for a range of aliphatic amines and anilines. Interestingly, the simplest primary amines (C₅, C₆, and C₁₀) tended to give slightly poorer yields, despite them being typically more active than aromatic systems. As expected in amide formation, selectivity was excellent. Other aliphatic acids were also screened with very good results, with secondary acids being slightly less reactive on steric grounds. Other strong solid acids were investigated with significantly lower conversions.

The same catalyst was utilised by Mesquita et al. in the acid‐catalysed Ritter reaction of steroids, again forming amide products [28]. Starting from epoxy steroids and acetonitrile, the authors found that Starbon‐400‐SO₃H catalysed the ring opening, and trapping of the resultant carbocation via hydration gave the resultant product as shown in Figure 3.7.

A series of different steroids was successfully functionalised in yields of 88–96%, with a lower yield of 60% being obtained with a steroidal epoxide of the opposite configuration to that shown in Figure 3.7. Similar yields were obtained when methylthioacetonitrile (MeSCH₂CN) was used, with the product being the MeSCH₂C(O)N‐product. With MeSO₂CH₂CN as the amide, oxazoline was formed by trapping of the intermediate carbocation (formed by attack of the nitrile on the protonated epoxide) by the vicinal hydroxy group.

Figure 3.6 Conversion of xylose to furfural and extraction of furfural.

Figure 3.7 Functionalisation of steroids via Starbon acid‐catalysed Ritter reaction.