3.3- Dimethyl-l,2-butanediol

As initiators usually serve Ziegler-Natta catalysts or Zn, Cd, Mg or A1 compounds [for example of the type Et2Zn + optically active (-)-3,3-dimethyl-l,2-butanediol]. The polymerizations are mostly heterogeneous. 

Methyl-l,2-pentanediol 3.3- Dimethyl-l,2-butanediol 4.4- Dimethyl-l,2-pentanediol 4- Methyl-l,2-hexanediol 5- Methyl-l,2-hexanediol 2-Methyl-2-propyl-l,3-propanediol 2-Ethyl-2-butyl-l,3-propanediol 2-Butyl-2-methyl-l,3-propanediol 2-Butyl-2-ethyl-l,3-propanediol 2,2-Dibutyl-l,3-propanediol... 

Sigwalt and coworkers noted higher stereoselectivity in the polymerization of propylene sulfide using a (f )-3,3-dimethyl-l,2-butanediol/ZnEt2 system when compared to a similar chiral alcohol/ZnEtz system. Based on these results, Sigwalt as well as others have applied this system to propylene oxide polymerization however, the observed stereoselectivity was actually lower than that for the polymerization of propylene sulfide. This lower stereoselectivity was presumably due to the... 

Optically active lactones are valuable building blocks in organic synthesis (4) and in the preparation of optically active biodegradable polymers (7,5). Several chemical methods for producing these compounds and their corresponding polymers have been explored (6) but unfortunately all of these methods are either experimentally cumbersome or afford the lactones with only modest enantioselectivities. Examples of chemically prepared optically active polyesters include poly(a-phenyl-P-propiolactone) (7), poly(a-ethy(-a-phenyl-P -propiolactone) (S, 9), poly(a-methyl-a-ethyl-P-propiolactone) (70) and poly(lactic acid) (77, 72). Use of enantioselective polymerization catalysts to carry out stereoelective polymerizations of racemic lactones has produced mixed results. For example, stereoelective polymerization of [/ ,S]- P-methyl-P-propiolactone with a catalyst from Zn ( 2115)2 and [7 ]-(-)-3,3-dimethyl-l,2-butanediol showed only a small enantiomeric enrichment in the final polymer (75). Stereoselective copolymerizations of racemic (LL/DD monomers) and meso (LD monomer) lactides using chiral catalyst that gives heterotactic and syndiotactic PLA, respectively have also been studied (77). 

In 1994, a highly efficient yttrium-based catalyst-yttrium 2-methoxyethoxide-was applied successfully to the polymerization of BL, with the reaction proceeding readily at room temperature [55]. When compared to diethylzinc/water or diethyl-zinc/methanol catalytic systems, the enantioasymmetric polymerization of racemic BL was also carried out in the presence of a diethylzinc/(R)-(-)-3,3-dimethyl-l,2-butanediol catalytic system (Scheme 9.18) [56]. 

For promoting penetration, the following polyol compounds are suitable (15) 2-Ethyl-2-methyl-l,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-l,3-propanediol, 2-ethyl-l,3-hexanediol, and 2,2,4-trimethyl-l,3-pentanediol. Among the above components, preferable examples include 2-ethyl-l,3-hexanediol and 2,2,4-tri-methyl-l,3-pentanediol. 

When an optically active alcohol is used for the preparation of the initiator, the polymerizations become of the enantioa-symmetrical type. The system diethylzinc/(l )-(-)-3,3-dimethyl-1,2-butanediol (1 1) has a high stereoelective nature for the polymerization of MT. ... 

From monomers with two chiral centers, optically active or racemic, (both in the heterocycle and in the lateral chain) different diastereoisomeric polymers can be obtained by classical or stereoelective processes. OA polythiiranes with two OA centers have been synthesized by a stereoelective polymerization of (+) or (-)A -methyl,A -sec-butyl,A-thiiranylamine using ZnEt2/( ) dimethyl-3,3-butanediol-l,2. The presence of an R) or (S) lateral chain has no influence on the stereoelection. In this case the thioether chromo-phore near the asymmetric carbon atom of the main chain becomes optically active and its contribution to the ORD curves is preponderant with no special conformational effect their characterization is now in progress [1 lOd]. 

Figure 2-47. La coupe du roi and the reaction sequence transforming cis-3,7-dimethyl-l,5-cyclooctanedione into 2-methyl-1,4-butanediol. After Cinquini et al. [77],...

Racemic 2,3-butanediol was converted to the racemic ditosy-late, which was then treated with catechol under the influence of NaOH in dimethylformamide (DMF) to yield the desired compounds, cis- and trans-2,3-dimethyl-l,4-benzodioxane [3] and [4]. The solid trans isomer [4] was obtained by repeated recrystallization from methanol. Column chromatography of the mother liquid using AloOj as adsorbent and petroleum ether and diethyl ether in a 1 1 ratio as eluent, gave pure liquid cis isomer [3]. By comparison with the PMR spectra (8) of pure trans- and cis-2,3-dimethyldi-oxane, the solid isomer was identified as trans, and the liquid isomer as cis. The compounds were further characterized by IR, NMR, CMR and elemental analyses. The CMR spectral data for 2 and 4 are summarized in Table I. 

Fragmentation processes of photoinitiators form a number of volatile products, which may contribute to indoor air pollution. Benzaldehyde and alkyl-substituted benzalde-hydes are usual components, because Norrish-I is the most important reaction for cleavage. Awell known example is l-phenyl-2-hydroxy-2-methyl-propane-l-one (PHMP). a-Cleavage generates two radicals in the first step. The benzoyl radical may recombine to form benzil, reduction of PHMP leads to l-phenyl-2-methy 1-1,2-propane and acetone, and recombination of the 2-hydroxypropyl radical gives 2,3-dimethyl-2,3-butanediol... 

The first chemical analog of la coupe du roi was demonstrated by Cin-quini et al. [2-58] by bisecting the achiral molecule cij-3,7-dimethyl-l,5-cyclooctanedione into homochiral halves, viz., 2-methyl-1,4-butanediol. The reaction sequence is depicted in Figure 2-57 after Cinquini et al. [2-58], who painstakingly documented the analogy with the pomaceous model. Only examples of the reverse coupe du roi had been known prior to the work of Cinquini et al. Thus, Anet et al. [2-57] had reported the synthesis of chiral 4-(bromo-methyl)-6-(mercaptomethyl)[2.2]metacyclophane. They then showed that two homochiral molecules can be combined to form an achiral dimer as shown in and illustrated by Figure 2-58. 

Aliphatic Glycidyl Ethers. Aliphatic epoxy resins have been synthesized by glycidylation of difunctional or polyfunctional polyols such as a 1,4-butanediol, 2,2-dimethyl-l,3-propanediol (neopentyl glycol), polypropylene glycols, glycerol, trimethylolpropane, and pentaerythritol. 

Polyester-Polyether Thermoplastic Elastomers Dimethyl Terephthalate/l,4-Butanediol/Dihydroxy-Poly(oxytetramethylene)... 

About 30 years ago, an enthalpy of formation was reported for 3,3,4,4-tetramethyl-l,2-dioxetane . Both by direct microcalorimetric combustion measurements of the neat solid and by reaction calorimetry (of the solid itself, and in acetone solution to form acetone), a consensus value was derived. Now, is the enthalpy of formation plausible , notwithstanding the very large error bars Consider reaction 6 for the dioxetane that produces 2,3-dimethyl-2,3-butanediol . The liquid phase enthalpy of reaction is —329 kJmoU. It is remarkable that this value is compatible with that for the dialkyl peroxides, ca —335 kJmoU, despite the ring strain that might be expected. 

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