tetrachloride molecule Poisonous plume of smoke

Haloalkanes. Preparation of haloalkanes. You will:know what haloalkanes areknow the preparation of haloalkanes Haloalkanes Haloalkanes (alkyl halides) are the saturated aliphatic organic compounds that contain “carbon-halogen” bonds in their composition.Haloalkanes are very important for the synthesis of many compounds. Replacement of hydrogen atoms with halogen makes the compound chemically active, since the bond of carbon with the more electronegative halogen atom is polar and quite reactive in ion-type reactions. The polarity of a covalent bond, for example C-Cl, leads to a shift in the electron density of neighboring bonds in the molecule. Physical properties of haloalkanes Most halooalkanes in pure form are colorless compounds. Physical properties depend not only on the alkyl group to which the halogens are bound, but also on the halogen itself and the number of its atoms in the molecule.Haloalkanes are insoluble in water, but soluble in organic solvents. Halogen-metanes are gases (except iodomethane) and have a sharp odor.For halooalkanes, the following regularities in the variation of physical properties can be distinguished:1. In the transition from primary to secondary and tertiary halogenoalkanes with the same number of carbon and halogen atoms, the boiling points and the density of matter increase.2. As the number of halogen atoms increases, the melting and boiling temperatures of the compound increase, which is natural, since the molecular weight of the compounds increases sharply (halogen atoms are “heavy” atoms), except polyfluorinated alkanes.3. A feature of the physical properties of haloalkanes is a reduction in the melting and boiling point of a compound containing 2 or 3 halogen atoms per carbon atom, as compared to an isomer having halogen atoms for different carbon atoms.4. In general, iso-structured haloalkanes have lower melting and boiling points than their isomers of normal structure. Physical properties of haloalkanesCompoundBoiling point (oC)Methyl chloride CH3Cl-24Dichloromethane CH2Cl240Trichloromethane (chloroform) CHCl361Tetrachloromethane CCl477 Physical properties of haloalkanesCompoundStructural formulaMelting point (oC)Boiling point (oC)FluoromethaneCH3-F-141,8-78,5ChloromethaneCH3-Cl-97,7-23,7BromomethaneCH3-Br-93,73,6IodomethaneCH3-I-66,542,5554555956   Chloroform molecule Carbon tetrachloride molecule Poisonous plume of smoke at Hawaii’s Kilauea Volcano. Chloromethane (CH3Cl) is also found in emissions from volcanoes such as Hawaii’s Kilauea. Preparation of haloalkanes Methods for the preparation of alkane halides can be combined into two groups: substitution reactions and addition reactions. The method of preparation and reaction conditions depend on the structure of the carbon skeleton of the halogenated molecule and that atom or group of atoms that are subjected to substitution (outgoing groups).Halogenation of alkanes  Halogenation of alkanes is a substitution reaction of one or more hydrogen atoms in an alkane molecule by halogen. The reaction products are called haloalkanes or halogenated alkanes. The reaction of alkanes with chlorine and bromine goes on light or with heating.  CH4 + Cl2 CH3Cl + HCl (hv – quantum of light)    chloromethane With a sufficient amount of chlorine, the reaction proceeds further and leads to the formation of a mixture of substitution products of 2, 3, and 4 hydrogen atoms:  CH3Cl + Cl2 CH2Cl2 + HCl      dichloromethane  C2H2 + Cl2 CHCl3 + HCl trichloromethane  CHCl3 + Cl2 CCl4 + HCl   tetrachloromethane The reaction of halogenation of alkanes proceeds via a radical chain mechanism, i.e. as a chain of successive transformations involving free-radical particles. The mechanism of radical substitution (symbol SR)Step 1: Nucleation of the chain – the appearance of free radicals in the reaction zone. Under the action of light energy, the bond in the molecule Cl:Cl is homolytically destroyed by two chlorine atoms with unpaired electrons (free electrons) Cl: Step 2: Growth (development) of the chain. Free radicals, interacting with molecules, generate new radicals and develop a chain of transformations: Step 3: ?hain termination. Radicals, connecting with each other, form molecules and terminate the chain of transformations: In the chlorination or bromination of an alkane with secondary or tertiary carbon atoms, hydrogen is most easily replaced by a tertiary atom, more difficult for a secondary one, and even more difficult for a primary one. This is explained by the greater stability of tertiary and secondary hydrocarbon radicals compared with the primary ones due to delocalization of the unpaired electron. Therefore, for example, with bromination of propane, the main reaction product is 2-bromopropane:2. Hydrochlorination of unsaturated hydrocarbons: CH2 = CH2 + HCl ? CH3Cl3. Obtaining from alcohols: CH3OH + HCl ? CH3Cl + H2O Dichloromethane, trichloromethane and tetrachloromethane are used as organic solvents Halothane (CF3CHClBr) and Forane (CF2HOCClHCF3) are used in medicine as an anestetic.   667246678              182781032