Ketene dimers

Submitted by Jonathan W illiams and John A Krymtsky. Checked by Nathan L Drake and Josi 1 h Lann 

Three 300-cc. gas-washing cylinders (Note 1) are connected in series, and the second and third cylinders are charged with 150 cc. each of dry acetone. Each of the three cylinders is immersed, in a thermos bottle, in sufficient Dry Ice-acetone cooling mixture to cover half of the cylinder. Ketene gas, prepared by the pyrolysis of acetone (Note 2), is passed through the system (Note 3) until a quantity of 2 moles has been introduced. This 

The liquids from all three cylinders are combined and fractionally distilled (Note 4). Most of the acetone is removed at room temperature under a pressure of 20 mm the last small portion is removed under atmospheric pressure. When the distillation temperature reaches 120°, the system is evacuated to a pressure of 80-100 mm. (Note 5), and the ketene dimer is collected within the boiling range 67-69°/q2 mm. The yield of pure product is 42-46 g. (50-55 per cent of the theoretical amount) (Notes 6 and 7). 

The gas-washing cylinders are preferably without flanges. Those used by the submitters were prepared from 45-mm. Pyrex tubing, measured 28 cm. in length, and were fitted with 29/42 standard taper ground-glass joints. The inlet tubes extended two-thirds of the way into the cylinders. 

Ketene may be generated conveniently from acetone by means of a ketene lamp. 1 This apparatus was used by submitters and checkers. Other apparatus (Org. Syn. Coll. Vol. 1, 324) might also be used. 

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Ketene Process. The ketene process based on acetic acid or acetone as the raw material was developed by B. F. Goodrich (81) and Celanese (82). It is no longer used commercially because the intermediate P-propiolactone is suspected to be a carcinogen (83). In addition, it cannot compete with the improved propylene oxidation process (see Ketenes, ketene dimers, and related substances). 

Higher dimeric ketenes are flammable but have higher flash points and are less reactive than diketene. Almost no data are available. Diketene can be disposed of by incineration, preferably after dilution with an inert solvent such as toluene. Higher ketene dimers can also be incinerated. 

Internal Sizing. The most widely used internal sizes are alkyl ketene dimers (AKD), alkenylsuccinic anhydrides (ASA), and rosin-based sizes that are used with papermaker s alum (aluminum sulfate with 14 waters of hydration), polyaluminum chloride (PAG), or polyaluminum siUcosulfate (PAS) (61). The rosin-based sizes are used under acidic conditions. Since the mid 1980 s there has been a steady conversion from acid to alkaline paper production, resulting in static to declining demand for the rosin-based sizing systems. Rosin is a complex mixture of compounds and consists primarily of monocarboxyhc acids with alkylated hydrophenan threne stmctures (62). A main constituent of wood rosin, gum rosin and taH-oil rosin is abietic acid. 

Two extreme mechanisms can be envisaged (Scheme 12), concerted [2 + 2] cycloaddition or the more generally accepted formation of a dipolar intermediate (164) which closes to a /3-lactam or which can interact with a second molecule of ketene to give 2 1 adducts (165) and (166) which are sometimes found as side products. In some cases 2 1 adducts result from reaction of the imine with ketene dimer. 

On the other hand y-pyrones or 1,3-diketones could be obtained from the reactions of ketone derived enamines with diketene 423-426). The addition of dimethyl ketene dimer to aldehyde or ketone derived enamines produced cyclohexanediones 425,426). 

The diion mechanism c has been reported for at least some of the reae-tions in categories 3 and as well as some ketene dimerizations. For example, the rate of the reaction between l,2-bis(trifluoromethyl)-l,2-dicyanoe-thene and ethyl vinyl ether was strongly influenced by changes in solvent polarity.Some of these reactions are nonstereospecific, but others are stereo-specific. As previously indicated, it is likely that in the latter cases the di-ionic... 

This dimerization is so rapid that ketene does not form P-lactones with aldehydes or ketones, except at low temperatures. Other ketenes dimerize more slowly. In these cases the major dimerization product is not the P-lactone, but a cyclobutanedione (see 15-61). However, the proportion of ketene that dimerizes to p-lactone can be increased by the addition of catalysts such as triethylamine or triethyl phosphite. Ketene acetals R2C=C(OR )2 add to aldehydes and ketones in the presence of ZnCl2 to give the corresponding oxetanes. ... 

Ketenes can be prepared by treatment of acyl halides with tertiary amines. The scope is broad, and most acyl halides possessing an a hydrogen give the reaction, but if at least one R is hydrogen, only the ketene dimer, not the ketene, is isolated. However, if it is desired to use a reactive ketene in a reaction with a given compound, the ketene can be generated in situ in the presence of the given compound. ... 

Monosubstituted ketenes dimerize into 1,3-cyclobutandiones. The regioselectivity is believed to be determeined by the steric repulsions of the substituents. Catalysts change the regioselectivity. 

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