Alkyl halides boiling point

Table 4 2 lists the boiling points of some representative alkyl halides and alcohols When comparing the boiling points of related compounds as a function of the alkyl group we find that the boiling point increases with the number of carbon atoms as it does with alkanes... 

For a discussion concerning the boiling point behavior of alkyl halides see the January 1988 issue of the Journal of Chemical Education pp 62-64... 

Boiling Points of Some Alkyl Halides and Alcohols... 

Solubility in Water Alkyl halides and alcohols differ markedly from one another m their solubility m water All alkyl halides are insoluble m water but low molecular weight alcohols (methyl ethyl n propyl and isopropyl) are soluble m water m all pro portions Their ability to participate m mtermolecular hydrogen bonding not only affects the boiling points of alcohols but also enhances their water solubility Hydrogen bonded networks of the type shown m Figure 4 5m which alcohol and water molecules asso ciate with one another replace the alcohol-alcohol and water-water hydrogen bonded networks present m the pure substances... 

This classical C-P bond-forming reaction (51) has seen limited application in the glyphosate arena, presumably for lack of suitable substrates that can tolerate the vigorous reaction conditions. Typically, C-P bond formation occurs when an alkyl halide reacts with excess neat trialkyl phosphite at temperatures exceeding 100 °C, near the boiling point of the phosphite. An Arbuzov-based strategy for glyphosate requires the synthesis of the... 

Problem 7.3 Compare and account for differences in the (a) dipole moment, (6) boiling point, (c) density and (d) solubility in water of an alkyl halide RX and its parent alkane RH. 

Coleman and co-workers36 performed a three-component reaction employing 2-oxothioacetamides, aldehydes and alkyl halides in ethanol with Na2 C03 as the catalyst to form a 24-member library of substituted 4-sulphonyl-l-ff-imidazoles (Scheme 5.20). The products were formed in yields of 40-96% and purities of 20-96%. The library was synthesised in a custom-built reaction block with expandable reaction vessels. The expandable reaction blocks were designed to accommodate the expanding gas volume caused by the elevated temperature without releasing any of it into the cavity. Unfortunately, this approach limited the temperatures used in the reactions to the boiling point... 

Upon completion of the reaction the reaction mixture was treated with a diluent which is a nonsolvent for PVC. Suitable diluents included aliphatic or aromatic hydrocarbons such as hexane, heptane, or benzene or compounds containing an active hydrogen atom such as acetic acid or a lower alkanol such as methanol or ethanol. Methanol was the preferred diluent by virtue of its miscibility with the preferred reaction medium (chlorobenzene), its ability to react readily with and deactivate an aluminum alkyl or alkylaluminum halide, and its low boiling point and water solubility. 

The physical properties of unsubstituted aryl halides are much like those of the corresponding alkyl halides. Thus, boiling points, melting points, and solubilities of aryl halides are very similar to those of alkyl halides containing the same number of carbon atoms. 

The polar C-X bond present in alkyl halides has a substantial dipole moment. Alkyl halides are poorly soluble in water, but are soluble in organic solvents. They have boiling points that are similar to alkanes of comparable molecular weight. Due to polarity, the carbon is an electrophilic centre and the halogen is a nucleophilic centre. Halogens are extremely weak nucleophilic centres and therefore, alkyl halides are more likely to react as electrophiles at the carbon centre. 

The reactivity of haloalkanes in alkylation reactions also decreases with increasing chain length. In general, syntheses of salts with short alkyl substituents are more complex due to the low boiling points of the haloalkanes. The most frequently used halide salt in this field, l-ethyl-3-methylimidazolium chloride ([EMIM] Cl), is typically synthesized in an autoclave with the chloroethane cooled to below its boiling point (12 °C) before addition. 

The carbon-halogen bond is slightly polar. Overall, however, an alkyl halide is not much more polar than an alkane, so the physical properties of an alkyl halide are not very different from those of an alkane of similar molecular weight. For example, the boiling point of 1-chlorobutane (MW = 92.5 g/mol) is 78°C, whereas that of hexane (MW = 86 g/mol) is 69°C. In general, alkyl halides are insoluble in water. Because of the presence of the more massive halogen atom, the alkyl halide may be more dense than water. For example, when dichloromethane, a common laboratory solvent, and water are mixed, two layers are formed, with dichloromethane as the lower layer. 

Table 6-2 also lists the densities of common alkyl halides. Like their boiling points, their densities follow a predictable trend. Alkyl fluorides and alkyl chlorides (those with just one chlorine atom) are less dense than water (1.00 g/mL). Alkyl chlorides... 

Dehydrohalogenatioiu Alkyl halides can be converted into alkenes by solid potassium 1-butoxide and a catalytic amount of 18-crown-6. Petroleum ether with a suitable boiling point range is used as solvent. No reaction is observed in the absence of a crown ether other bases (KOH, K2CO3) are ineffective. The method is particularly useful for dehydrohalogenation of primary alkyl halides, which are converted into ethers by potassium f-butoxide under usual conditions. ... 

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