2.4.6- trimethyl-l,3,5-trioxane

Paraldehyde (acetaldehyde trimer, 2,4,6-trimethyl-l,3,5-trioxane) 12,5 , 124 , d 0.995, n 1.407. Washed with water and fractionally distd. 

Paraldehyde (2,4,6-trimethyl-l, 3,5-trioxane) was claimed to behave in a similar way [582], An early German patent, published after Eckenroth s note [582], claimed that no reaction occurs between COClj and aldehydes at normal temperatures [612], and attempts to repeat Eckenroth s preparation [582] have not been successful [1763]. However, by combining the vapours of phosgene and ethanal at atmospheric pressure in a flow system over an activated charcoal catalyst, 1,1 -dichloroethane and carbon dioxide are found to be co-produced, especially in the temperature range of 150-200 "C [1753,ICI98,ICI99]. It was confirmed that no reaction occurs in the absence of a catalyst between 25 and 400 C [1763]. 

Polymerization. Paraldehyde, 2,4,6-trimethyl-l,3-5-trioxane [123-63-7], a cyclic trimer of acetaldehyde, is formed when a mineral acid, such as sulfuric, phosphoric, or hydrochloric acid, is added to acetaldehyde (45). Paraldehyde can also be formed continuously by feeding liquid acetaldehyde at 15—20°C over an acid ion-exchange resin (46). Depolymerization of paraldehyde occurs in the presence of acid catalysts (47) after neutralization with sodium acetate, acetaldehyde and paraldehyde are recovered by distillation. Paraldehyde is a colorless liquid, boiling at 125.35°C at 101 kPa (1 atm). 

TRIMETHYL-l,3,5-TRIOXANE (123-63-7) Forms explosive mixture with air (flash point 62°F/17°C). Reacts with strong acids, caustics, ammonia, amines, oxidizers. Decomposes on contact with acids or acid fumes, forming acetaldehyde. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

Using the rigid-rotor harmonic-oscillator approximation on the basis of molecular constants and the enthalpies of formation, the thermodynamic functions C°p, S°, — G° —H°o)/T, H° — H°o, and the properties of formation Af<7°, and log K°(to 1500 K in the ideal gas state at a pressure of 1 bar, were calculated at 298.15 K and are given in Table 9 <1992MI121, 1995MI1351>. Unfortunately, no experimental or theoretical data are available for comparison. From the equation log i = 30.25 - 3.38 x /p t, derived from known reactivities (log k) and ionization potential (fpot) of cyclohexane, cyclohexanone, 1,4-cyclohexadiene, cyclohexene, 1,4-dioxane, and piperidine, the ionization potential of 2,4,6-trimethyl-l,3,5-trioxane was calculated to be 8.95 eV <1987DOK1411>. 

If a mixture of 2,4,6-tri(l-methylethyl)-1,3,5-trioxane, trimethylsilyl isothiocyanate, and SnCl2 is stirred for 1.5 h at room temperature, 70% of the corresponding isothiocyanato substituted ether 0[CH(CH3)NCS]2 is obtained. 2,4,6-Trimethyl-l,3,5-trioxane was converted also into bis(l-isothiocyanatoethyl) ether in similar yield. However, 1,3,5-trioxane was recovered quantitatively under the same reaction conditions <1987BCJ2289>. 

Only a sparse amount of material has been published on this topic. Chlorination of 2,4,6-trimethyl-l,3,5-trioxane provided a mixture of chloroaldehydes which could be treated with concentrated sulfuric acid to yield 2,4,6-tri(chloromethyl)-l,3,5-trithiane 168 <1992CL171>. The corresponding dichlorination reaction catalyzed by SbCls at 80 °C (via the previously mentioned chloroaldehyde and hydrolysis to the hydrate) finally yielded the dichloro analog 167 (Scheme 44) <1993SC1289>. Actually, it is chlorination of 1,3,5-trioxane substituents via open-chain reactants that is the process in effect. 

The principal photochemical reaction of the 1,3,5-trioxane radical in freonic matrices at 77 K was studied carefully by ESR spectroscopy <2006M1259>, and the molecular interactions of 2,4,6-trimethyl-l,3,5-trioxane with -alkyl acetates <2006MI1664> and various carbonates <2006JCED69> and of 1,3,5-trioxane in the formaldehyde-water-... 

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