Diketene—acetone adduct

Six-membered heterocycles with two heteroatoms are prepared by reaction of diketene with a substrate containing a C—O or C—N multiple bond. With carbonyl compounds diketene reacts in the presence of acids to give l,3-dioxin-4-ones. The best known is 2,2,6-trimethyl-4H-l,3-dioxin-4-one [5394-63-8] (15), the so-called diketene—acetone adduct, often used as a diketene replacement that is safer to handle and to transport, albeit somewhat less reactive than diketene itself (103,104), forming acetylketene upon heating. 

A shippable but somewhat less reactive form of diketene is its acetone adduct, 2,2,6-trimethyl-4JT-l,3-dioxin-4-one (15) (103,104). Thermolysis of this safer to handle compound provides acetylketene, a reactive intermediate that can be used for acetoacetylation and cycloaddition reactions. The diketene—acetone adduct as weH as / fZ-butylaceto acetate [1694-31 -1] (also used for aceto acetylations by the trans aceto acetylation reaction) (130), are offered commercially. 

Diketene-acetophenone adduct. Mol. wt. 204.22, m.p. 93.5°. Preparation and use. see Diketene-acetone adduct. Supplier Aldrich. 

Amine End-group Modification with Diketene and Diketene Acetone Adduct... 

In this section, the blocking of the amine end groups of PA-6 with liquid diketene (the dimer of ketene) and the diketene acetone adduct (Fig. 13.8) in supercritical CO2 is discussed. Ketene itself is an extremely reactive, unstable, and very toxic gas. Diketene and the diketene acetone adduct have frequently been used in industry since they are reactive toward a large variety of functional groups such as amines, alcohols, and carboxylic adds [83-85], but are not reactive toward the amide groups in the PA-6 chain without a catalyst, whereas ketene is. This makes them useful for the modification of polymer partides in supercritical CO2 under very mild reaction conditions, thereby avoiding side reactions. 

In this section, the reactive reagent diketene and the somewhat less reactive diketene acetone adduct are impregnated into the polyamide granules, using pure CO2 as a carrier. Similar experimental conditions to those described for the amine end-group modification with SA (Section 13.3.2) were applied. 

Fig. 13.8 Structure of ketene, its dimer, and the diketene acetone adduct.

Comparing the results of the modification of PA-6 end groups with either succinic anhydride, 1,2-epoxybutane, or diketene and the diketene acetone adduct, it can be concluded that the optimal blocking agent must be small and must exhibit an intermediate reactivity toward the end groups in order to allow extensive penetration into the core of the granules before the blocking reaction starts to hinder further penetration. 

Petros and coworkers have reported the syntheses of seven- to nine-membered diaza heterocycles 101 in very high yields by reacting diketene—acetone adduct 99 and 1,2-, 1,3-, and 1,4-diamines 100 under solvent-free conditions and microwave irradiation (2014TL(55)6547). 

Pawloswski et al. described the s5mthesis of acetoacetoxypropyl cellulose (AAPC), formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct (2,2,6-trimethyl-4-H-l,3-dioxin-4-one) in A/-methyl-2-pyrrolidinone (NMP) at elevated temperature. The authors showed that as with APC, AAPC also forms both thermotropic and lyotropic liquid-crystalline phases. It is noteworthy to mention that the nematic to isotropic transition occurs at 174 °C and thin films of cholesteric thermotropic AAPC show green reflection colors (Pawlowski et al. 1986, 1987). 

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