Study Guides (238,408)
Canada (115,131)
Chemistry (192)
CHEM 222 (17)

CHEM 222 Lab Exam Notes.doc

5 Pages
Unlock Document

McGill University
CHEM 222
Mike Daoust

Lab 1 – Cycloadditon of Dichlorocarbene to Cyclohexene • Carbenes = intermediates with two single bonds and a pair of non- bonding electrons on a carbon. They lack a pair of electrons to complete a stable octet. • Carbenes are electrophilic and extremely reactive. • Can be done by thermal or photochemical decomposition of a diazo alkane (R 2=N =N ) to give the carbene and nitrogen (N ). 2 • Can be generated by carbanion alpha to an alykl halide, followed by alpha halide elimination. (Used to form dichlorocarbene by chloroform and a base: remove a proton, followed by alpha chloride elimination to give :CCl )2 Alpha elimination is the elimination of the alpha halide, to create the carbene. It is NOT PROTON ABSTRACTION. • In presence of an alkene, there is addition of the carbene to the double bond at the least substituted carbon. • Carbenes react readily with anion (negative charge) and nucleophiles. • A two-phase transfer catalyst was used as the organic phase had the alkene and carbene precursor, and the aqueous phase had the base. • A phase transfer catalyst: has good solubility in both organic and aqueous substances. Quaternary ammounium salts are frequently used (organic in the organic layer, ammonium group in the aqueous). Example: benzyltriethylammonium chloride, trioctylmethylammonium chloride and tetrabutylammonium sulfate. • The phase transfer catalyst is converted to its hydroxide salt in the presence of the base and this will equilibrate between the two layers. The reaction will only occur at the interphase of the reaction. • Used: NaOH (concentrated base 25M), chloroform (dichlorocarbene precursor), cyclohexene (alkene), benzyltriethylammnium chloride (phase-transfer catalyst), water, diethyl ether, • The phase transfer catalyst is hygroscopic, meaning it has the ability to attract and hold water molecules from the environment, and needs to be capped immediately and avoid contact with skin. • When shaking the separatory funnel to create the emulsion, wear gloves because the mixture is caustic, meaning it causes corrosion. • Any emulsion should be left in the AQUEOUS layer • The phase transfer catalyst promotes reaction at the interface, therefore an emulsion (a colloidal suspension of one liquid in another) was kept for a long time to increase yield (by shaking we increased the surface area). • It was washed with ether to dissolve any 7,7-dichloronorcane remaining in the aqueous layer because it is much more soluble in ether than in water. • After being dried with anhydrous sodium sulfate, it is Roto-vapped. At the point where it is evaporated down to 5-8mL, bubbles are no longer observed in the R.B flask. • Then subjected to simple distillation. At the final stage of simple distillation, the condenser was subjected to air-cooling instead of water because the final product apparently has very high boiling temperature and we might crack the condenser if we continue using water for cooling. o Vacuum on briefly, and then turned off, collect first distillate at variac setting of 45. When boiling slows, change receiver flasks, turn on vacuum fully, and set variac to 80. • The IR was taken to show a C-Cl stretch and no C=C. Things/techniques to know: Rotary-evaporation Lab 2 – The Grignard Reaction • Organometallic compound formed by reaction of an organic halide with magnesium in ether. • Grignard’s + aldehyde or ketone  secondary or tertiary alcohol and a new C-C bond. • The purpose of crushing the magnesium turning is to clean the surface and increase the active surface area of the turnings (removed MgO and grease) so the metal can react to form the Grignard reagent. • Saturated salt solution acts as a drying agent by removing aqueous residue from the ethereal solution. Anhydrous sodium sulfate also acts as a drying agent because it is hygroscopic and acts as a dessicant. • Wurtz coupling is the reaction between bromobenzene and Grignard reagent to form biphenyl. Biphenyl is soluble in hexane and is therefore removed as an impurity. Triphenylcarbinol is soluble in ether, but not hexanes. • Ether is used to stabilize the Grignard reagent, it is easy to Rotovap, it has a high vapor pressure (to keep water out), and helps to make the Grignard reagent soluble (therefore it goes from murky to brown). • A steam bath is used since ether is extremely flammable, so it is safer. • Anhydrous diethyl ether (absolute ether) is used and not petroleum ether (mixture of alkanes) or regular ether (has water). • Ether is added in two steps because the higher the concentration of reactants, the more rapid the reaction (you don’t want to dilute the reactants too early). • 10% sulphuric acid and water are used to quench the reaction by protonating the oxygen to make alcohol. • Solid product, took the melting point and predicted purity. Lab 3 – Oxidation of an Alcohol• Primary and secondary alcohols can be converted back to aldehydes and ketones respectively, by oxidation. • Care must be taken when converting a primary alcohol to an aldehyde, so it is not further oxidized to a carboxylic acid. This can be done by removing the aldehyde as it is formed • A secondary alcohol can ONLY be made into a ketone. • Four oxidizing mixtures are commonly used: o Permanganate in basic solution (often potassium permangante in sodium hydroxide, is a very strong oxidizer and produce a carboxylic acid to primary alcohols, but still a ketone for secondary alcohols. o Chromic acid in water or acetic acid is a strong oxidizer, but primary alcohols converted to aldehydes must be removed as they are formed. o Chromic acid in aqueous acetone
More Less

Related notes for CHEM 222

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.