Isopropenyl Acetate for the Continuous-Flow Synthesis of Triacetin, Solketal Acetate, and Allyl Acetate from Pure or Crude Glycerol

Isopropenyl acetate(iPAc) proved to be an effective green reagentfor the chemical upgrading of refined and crude glycerol (CG) intovaluable products, such as allyl acetate, triacetin (TA), and acetalacetates, under continuous-flow (CF) conditions. Two unprecedentedtandem catalytic protocols of deoxydehydration (DODH)/acetylationand acetylation/acetalization were implemented to convert glycerolinto allyl acetate and acetal acetates. These products were achievedin 95 and 78% yields, respectively, by combining a pool of innocuouscompounds that acted with different roles: iPAc as an acetylatingagent, triethylorthoformate as a DODH agent, acetone as an acetalizationagent, and acetic acid and Amberlyst-15 as the homogeneous and heterogeneouscatalysts, respectively. The parametric analysis of the process variablesallowed us to reach the productivity (P) of 10.6mmol center dot h(-1) mL(-1) at 300 degrees Cand 110 bar and 37 mmol center dot g(cat) (-1) h(-1) at 30 degrees C and ambient pressure for the (DODH)/acetylationsequence and the acetylation/acetalization cascade reaction, respectively.Acetal acetates were obtained as a mixture of (2,2-dimethyl-1,3-dioxolan-4-yl)methylacetate (solketal acetate) and 2,2-dimethyl-1,3-dioxan-5-yl acetatein a 97:3 ratio. A third protocol was designed for the peracetylationof CG as an industrial waste with iPAc: in the absence of any catalyst,TA (glycerol triacetate) was isolated in 92% yield with the productivityimproved by more than 60 times compared to previous literature results.The performance of two of the target products (acetal acetates andTA) as biofuel additives was also investigated. Two tandem sequences of deoxydehydration/acetylationandacetylation/acetalization and a peracetylation reaction, all mediatedby isopropenyl acetate, prove excellent for the conversion of glycerolinto allyl acetate, acetal acetates, and triacetin.

Automated summary

Isopropenyl acetate (iPAc) can convert refined and crude glycerol (CG) into valuable products, such as allyl acetate, triacetin (TA), and acetal acetates, under continuous-flow conditions. This study presents two novel tandem catalytic protocols that achieve high yields of these products by using a combination of innocuous compounds with different roles. The importance of this research lies in providing a green and efficient method for the chemical upgrading of glycerol into valuable products, and improving the yields by optimizing process variables and catalyst selection.