Grignard Synthesis of Triphenylmethanol Lab Report Essay Example

with water to produce alkanes. This is the reason that everything has to be very dry during the preparation. Alkyl halides vary greatly in their rates of reaction with magnesium. For example, alkyl iodides generally react very rapidly, whereas most aryl chlorides react very slowly, if at all.

Their chemical behavior resembles that of carbanion species that contain a negatively charged carbon (:CH3-). Grignard reagents are strong bases and strong nucleophiles. Thus, the Grignard reagent methylmagnesium bromide (CH3MgBr) behaves as if it were equivalent to the methide ion (:CH3-). Grignard reagents are made through single electron transfers with magnesium and an alkyl halide. Grignard reagents are manufactured through the process of a radical reaction as shown below.

Grignard reagents react with molecules to extend carbon-carbon chains through the attraction of a nucleophilic carbon to an electrophilic carbon (nucleophilic addition). The Grignard reagent can serve as a nucleophile because of the attraction between the slight negativeness of the carbon atom in the Grignard reagent and the positiveness of the carbon in the carbonyl compound. The Grignard reagent can oxidize a carbonyl functional group into a hydroxyl group. The metal is less electronegative than the carbon, so the carbon bears a partial negative charge.

This partial negative charge attacks the carbonyl at the partially positive carbon, forms a new carbon-carbon bond, and pushes an electron pair out of the double bond into the lone pair position. The metal then attaches itself at the now negatively charged oxygen. This compound is then treated with an aqueous acid to protonate the oxygen and forms the hydroxyl group. Except for hydrocarbons, ethers, and tertiary amines, almost all

organic compounds react with Grignard reagents.

Many of these reactions are used for synthetic purposes, notably those with carbonyl compounds (e. g. aldehydes, ketones, esters, and acyl chlorides), with epoxides, and with halogen compounds of certain metals (e. g. , zinc, cadmium, lead, mercury) to form the alkyl derivatives of those metals. Grignard reagents react with water to form a strong base, and they can act as a nucleophile to find a primary alcohol as shown respectively below. Grignard reagents also react with the least hindered carbon on an epoxide to break the ring in order to relieve ring strain. A reaction of the Grignard reagent and carbon dioxide results in an acid, and reaction of a nitrile and a Grignard reagent produce a carbonyl via an imine intermediate.

These are show below, respectively. Grignard reagents are reactive enough to also attach esters; however, two equivalents of the Grignard reagent are usually added because less then two equivalents leave a large quantity of unreactive ester. This reaction forms a tertiary alcohol. Grignard reagents cannot be synthesized from alcohols because instead of reacting with the halide to form the Grignard reagent, the alcohol is deprotenated. Grignard reagents also cannot be synthesized from molecules with a carbonyl group. Solvent choice is important in Grignard reagent formation.

The solvent must be non-reactive with a negatively charged carbon (ex. acetone or anything even slightly acidic), and the solvent cannot have a carbonyl group. The solvent must be a volatile solvent that provides a blanket of solvent over the reaction solution so that oxygen and moisture in the air are excluded from the reaction. Oxygen and moisture

in the air are very slightly acidic and would disrupt the synthesis of a Grignard reagent. Anhydrous ether (R2O) is often used as a solvent in creating Grignard reagents because it keeps out water and oxygen, makes the complex soluble, and is non-reactive.

Water and oxygen cause undesired side reactions. The oxygen in ether has a lone pair of electrons, which is attracted to the partially positive metal. The solvent helps the polar Grignard reagent dissolve by coordination. A dry reflux apparatus is used to heat a solution without gaining any water from the atmosphere. Reflux is the cycle of a liquid going through vaporization and condensation. In order to speed up reactions or to increase the solubility of a compound, chemists often times reflux reaction mixtures. This step implies that the reaction mixture is brought to a boil.

The lowest boiling compound in the mixture determines the temperature when this occurs, usually the solvent. It condenses and returns into the reaction vessel (3). There are some other benefits to using a reflux apparatus. First, molecules dissolve faster in heated liquids because the molecules are moving faster and thus collide faster and more often. Second, the heat needed to cause the solution to reflux is energy that can assist molecules in acquiring enough energy to overcome the activation energy barrier to go from liquid to vapor.

The liquid in the flask boils, vaporizes, and then hits the cool condenser and condenses back into the flask. The water running through the condenser keeps it cool and allows the vapors rising out of the reaction vessel to condense and drip back down into the

solution. The CaCl2 in the drying tube keeps any water from the atmosphere from entering the system. The set up of a dry reflux apparatus is a round bottom flask clamped above a heating mantle with a condenser attached to the round bottom flask. A thermometer adapter is used to attach the drying tube to the condenser. The entire apparatus is clamped to the bars to keep it stable.