CHEM 233: Post Midterm Procedures and Purpose of each Reagent

Sn2 (halogenation of alcohol) procedure

1. add butanol and sodium bromide and water to round bottom and dissolve (water to free Br ions)

2. put on ice (exothermic to add acid), add H₂SO₄ (to protonate butanol)

3. reflux

4. simple distillation — collect until 115C (close to butanol boiling point)

5. wash with water (organic on bottom, 1.28)

6. wash with concentrated sulfuric acid, then NaOH, then water, then brine

7. dry with Na₂SO₄

Sn1 (dehydration of alcohol) procedure

1. combine 2-methyl-2-butanol with HCl in separatory funnel

2. keep organic layer (top — density .86)

3. wash with brine, then cold NaHCO₃, water, brine

4. dry organic layer with na2so4

5. simple distillation — keep fraction with boiling point above 75C (BP of prod is 85)

Sn2 butanol

electrophile

Sn2 NaBr

nucleophile

Sn2 water

solvent

Sn2 sulfuric acid

protonate alcohol

Sn2 wash with sulfuric acid

dry

Sn2 wash with NaOH

neutralize H2SO4

Sn2 wash with water

separate organic and aqueous

Sn2 wash with brine

separate organic and aqueous

Sn1 2-methyl-1-butanol

electrophile

Sn1 HCl

nucleophile

Sn1 wash brine

separate organic and aqueous

Sn1 cold sodium bicarbonate

neutralize excess acid (can’t use NaOH because that would do E2 reaction)

Sn1 wash water

separate aqueous and organic

Sn1 wash brine

separate organic and aqueous

Silver Nitrate Test — what does it test for / visual change

the substitution of your product — white precipitate in ethanol if tertiary or secondary

Silver Nitrate Test — reagents/mechanism

AgNO3 in ethanol

• Sn1 “like” mechanism

• Ag+ is a good lewis acid — it pulls Cl or Br (lewis bases) off of carbon chain

• Nitrate is nucleophile and takes place of Cl or Br

• AgCl / AgBr wil ppt in ethanol

Sodium Iodide Test — what does it test for / visual change

the substitution of your product — clear to white ppt in acetone if primary or secondary

Sodium Iodide Test — reagent and mechanism

NaI in acetone — Sn2 “like” mechanism

• Iodide attacks electrophilic carbon, Cl or Br leaves

• Resulting NaCl or NaBr precipitates in acetone

E2 (elimination to form alkene) procedure

1. KOH + propanol (solvent) in roundbottom flask

2. warm gently to dissolve (volatile so cover with watch glass), put on ice when dissolved

3. add 2-chloro-2-methyl butane

4. grease joints, reflux for hour (with raschig rings in hempel column)

5. fractional distillation — collect on ice until 45 C (alkene has much lower boiling point than alcohol — we don’t want to accidentally collect alcohol too)

6. keep on ice

E1 procedure (acid catalyzed elimination to form alkene) procedure

1. 2-methyl-2-butanol + H₂SO₄ in round bottom flask

   1. sulfuric acid protonates 2-methyl-2-butanol

   2. water deprotonates the carbocation to form the alkene

2. fractional distillation — collect on ice until 45 C

We are distilling products away from starting materials as they form, since alkene boiling point is well below alcohol boiling point

E2 2-chloro-2-methyl butane

electrophile

E2 KOH

base / nucleophile (deprotonates electrophile)

E2 propanol

solvent (polar, aprotic)

E1 2-methyl-2-butanol

electrophile

E1 H₂SO₄

acid that catalyzes elimination — protonates alcohol so group can leave and deprotonates the carbocation

Bayer Test — what does it test for / visual change

• checks for presence of alkenes

• Purple → brown if alkene present

Bayer test — reagents / mechanism

KMnO₄ (potassium permanganate)

• KMnO₄ is purple

• if alkene is present, results in vicinal diol (colorless) and Manganese Dioxide (brown)

• So, brown = presence of alkene

Bromine test — what does it test for / visual change

• tests for presence of alkenes or alkynes

• bromine is orange, if alkene present, goes clear (vicinal dihalide)

Bromine test — reagents / mechanism

Br₂

• if alkene present, bromine adds across alkene

• forms vicinal dihalide (colorless)

Bayer test — procedure

• make 3 test tubes with water

• add 1-2 drops of each product in the corresponding tube, with 1 control

• add a couple drops of KMnO₄

Bromine test - procedure

• fill 3 tubes with 1mL ethyl acetate (or DCM) in each

• add 1-2 drops of each product in the corresponding tube, with 1 control

• add a couple drops of Bromine to each

Pinacol → Pinacolone Procedure

1. add pinacol (solid) and sulfuric acid to round bottom flask

2. simple distill (“the ketone-water azeotrope”) 20-25 mL on ice

3. separate organic (top, 0.8) and aqueous layers

4. wash aqueous twice with hexanes (top, 0.66) to get any remaining organic out

5. combine all organic layers and wash with 10% sodium bicarbonate (neutralize any excess acid)

6. dry with Na₂SO₄

7. rotovap

Pinacolone → Semicarbazone procedure

1. in test tube, combine semicarbizide hydrochloride, sodium acetate, and water

2. add pinacolone (if not soluble in water, add ethanol to dissolve first)

3. shake vigorously

4. cool on ice to white ppt

5. workup: vaccum filter (isolation), washing with cold water (purification)

6. melting point

lab 8 — pinacol

substrate

lab 8 — sulfuric acid

protonates pinacol so H₂O leaves

lab 8 — hexanes wash

use hexanes to extract organic from aqueous layer

lab 8 - wash NaHCO₃

neutralizes acid

lab 8 — pinacolone

substrate / electrophile

lab 8 - semicarbazide HCl

nucleophile (attacks C in ketone)

lab 8 - sodium acetate

deprotonates semicarbazide HCl making it nucleophilic (“activates” it)

Iodoform test — what does it test for / visual change

• checks for presence of methyl directly adjacent to carbonyl

• brown basic iodine solution + ketone → canary yellow solid (iodoform)

Iodoform test — reagent / mechanism

• basic iodine solution = I₂ + NaOH

• you need a ketone where one side is a methyl group

• OH deprotonates methyl group, leaving negatively charged carbon

• negatively charged carbon grabs I from I₂

• repeat 3x

• attack carbon’s C with -OH, makes negatively charged O

• push e- from neg charged O back down, pushing of CI₃ where C is negatively charged

  • makes neg charged Iodoform and carboxylic acid

• C in iodoform deprotonates carboxylic acid

  • Iodoform is yellow

Product: Iodoform

Byproducts: Sodium acetate, Sodium iodide, water

Iodoform test — procedure

1. combine about 2mL of water with pinacolone

2. add NaOH

3. add I₂ / KI solution dropwise until yellow ppt formed — yellow ppt = positive result

there’s more but idk what or why — see page 143 in manual

CAN Test — what does it test for / visual change

• tests for OH group

  • forms distinct complexes with OH groups (whether alcohol, diol, carb, etc.) — diff shades of red

  • CAN test with alcohol → magenta

• yellow → red if OH present

CAN Test — reagents/mechanism

CAN reagent = yellow solution of diammonium hexanitratocerate (IV) in dilute nitric acid

• color change comes from changing groups attached to certain inorganic ions (like Ce) which cause changes in electronic structure

CAN Test — procedure

• put starting alcohol in one tube, pinacolone in the other

• add drops of CAN — if red, OH present

• (we want no OH) so goal is product vial stays yellow

Reduction of fluorenone to fluorenol — procedure

1. add 9-fluorenone and methanol to flask. heat gently to dissolve

2. cool to room temp

3. add Sodium Borohydride. stir vigorously. H₂ forms. do not stopper

4. leave to stand at room temp. should be colorless

5. take TLC w/ fluorenone, cospot, reaction mixture

6. work-up — add H₂SO₄, heat gently to dissolve any solid formed, cover with watch glass

7. solid should ppt on ice

8. vacuum filter, wash with water until pH of water exiting funnel is neutral

9. recrystallize with methanol