CHEM 31.1 REVIEWER EXPERIMENT 1 – SOLUBILITY BEHAVIOR OF ORGANIC COMPOUNDS
Solubility is related or dependent to the functional group attached in your compound. Functional group dictates H-bonding capability, acidity, and basicity of the compound. CLASS S – water soluble compounds; H-bonding IMF electronegative group attached to H.
-OH, -NH2, -COOH, -CONH2
Example: Low MW amines, low MW carboxylic acids, low MW neutral compounds.
CLASS S1 – slightly soluble in water; soluble in ether; few H-bonding groups; has significant Van der Waals interaction
Ethanol and acetone
Acetone + Ether (Dipole-Dipole) Ethanol + Ether (Dipole-Dipole)
CLASS S2 – very or highly soluble in water; many H-bonding sites; dissolve poorly in ether Sucrose (C12H22O11)
CLASS A – acidic compounds or have acidic functional groups; H+ is easily donated to a base CLASS A1 – strong acids; dissolves in both NaOH and NaHCO3
Example: Compounds containing carboxylic group, carboxylic acid and phenol with electron withdrawing groups (NO2 and halides)
CLASS A2 – weak acids; dissolves only in NaOH
Example: Phenol without electron withdrawing groups.
CLASS B – basic compounds usually have N which has a basic electron pair Examples: Amines
CLASS M – miscellaneous neutral compounds; have N but not basic; have S but not acidic
Example: Benzamide, amides or compounds containing nitro groups, benzaldehyde, benzyl alcohol
CLASS N – neutral compounds; compounds reactive with H2SO4 (forced protonation); oxygen-containing compounds (not very basic pi electrons); unsaturated compound
Example: esters, aldehydes, alkenes, alcohols, ketone
CLASS I – inert compounds; very unreactive/ very stable compounds; do not react with concentrated H2SO4; saturated compounds, saturated hydrocarbons, and aromatic hydrocarbons
Example: hexane, toluene, tert-butylchloride SOLUBILITY CLASSIFICATION
The identification of an unknown organic compound can be greatly assisted if it is first assigned to a solubility class. Following is a brief description of each of the eight classes.
Class S1. Compounds soluble in water and ether. Typically these are compounds of low molecular weight, with the exceptions of low-molecular-weight hydrocarbons and their halogen derivatives (Class I). Low-molecular-weight compounds that have two or more functional groups usually belong in Class S2
Class S2. Compounds soluble in water and insoluble in ether. Typically these include water soluble salts and most of the low-molecular-weight bi- and poly-functional compounds.
Class A1. Compounds insoluble in water but soluble in sodium hydroxide solution and in sodium bicarbonate solution. Acids (eg benzoic acid) and a few phenols (eg picric acid, s-tri-bromophenol).
Class A2. Compounds insoluble in water and in sodium bicarbonate solution, but soluble in sodium hydroxide solution. Weakly acidic compounds such as oximes, amino acids,
sulfonamides of primary amines, primary and secondary nitro compounds, enols, most phenols, and certain thiols belong in this class.
Class B. Compounds, insoluble in water and in alkali, which react with dilute hydrochloric acid to yield soluble products. Amines are in this class but di- and tri-arylamines are exceptions (class N). Water soluble salts of weak acids such as calcium oxalate and certain acetals, which are readily hydrolyzed by dilute acids, may also fall in this class.
Class N1. Neutral compounds insoluble in water and soluble in sulfuric acid and in
phosphoric acid. Low molecular weight alcohols, aldehydes, cyclic ketones, methyl ketones and esters make up this class. Typically compounds in this class contain nine carbon atoms, or fewer.
Class N2. Neutral compounds insoluble in water and in syrupy phosphoric acid and soluble in sulfuric acid. In addition to alcohols, aldehydes, ketones and esters which have more than nine carbon atoms this class also contains many quinones, ethers, and unsaturated
hydrocarbons, and some anhydrides, lactones, and acetals (the latter 3 groups may also be found in S1 and N1).
Class I. Compounds, insoluble in water, which dissolve in none of the other solvents.
Typically these include saturated aliphatic hydrocarbons, aromatic hydrocarbons, and their halogen derivatives.
Class Functional Group Possibilities
Sa monofunctional carboxylic acids (≤5C), arylsulfonic acids Sb monofunctional amines (≤6C)
Sg monofunctional alcohols, aldehydes, ketones, esters, nitriles, and amides (all ≤5C) S salts of organic acids, amine hydrochlorides, amino acids, polyfunctional compounds with hydrophilic functional groups
As strong organic acids: carboxylic acids (>6C), phenols with electron-withdrawing groups in the ortho and/or para position(s), b-diketones
Aw weak organic acids: phenols, enols, oximes, imides, sulfonamides, thiophenols (all >5C), b-diketones, nitro compounds with a-hydrogens B aliphatic amines (≥8C), anilines (only one phenyl group attached to N), some ethers Nm miscellaneous neutral compounds containing N or S (>5C)
N alcohols, aldehydes, ketones, monofunctional esters (>5C but <9C), ethers, epoxides, alkenes, alkynes, some aromatic compounds (with activating groups)
I saturated hydrocarbons, haloalkanes, aryl halides, other deactivated aromatic compounds, diaryl ethers
Sa They are soluble in water and ether because they contain both polar and non-polar functional groups. They are red to litmus because their pH is below 4.5.
Sb They are soluble in water and ether because they contain both polar and non polar functional groups. They are blue to litmus because their Ph is above 8.3.
S1 They are soluble in water and ether because they contain both polar and non polar functional groups. They are neutral to litmus because their pH fall within the range 4.5<pH<8.3.
S2 They are soluble in water but insoluble in ether because they are too polar to dissolve in the latter.
A1 They are insoluble in water due to the dominance of their non-polar groups. They are soluble in 5% NaOH because they contain an acidic functional group and in 5% NaHCO3 because their acidity is strong enough to react with a weakly basic solvent.
A2 They are insoluble in water due to the dominance of their non-polar groups. They are soluble in 5% NaOH because ether contains an acidic functional group but are insoluble in 5% NaHCO3 because their acidity is insufficient to react with a weakly basic solvent. B They are insoluble in water due to the dominance of their non-polar groups. They are
insoluble in 5% NaOH because they do not contain an acidic functional group but are soluble in 5% HCl due to their basicity inaqueous solutions.
MN They are insoluble in water due to the dominance of their non-polar groups. They are insoluble in 5% NaOH and 5% HCl becausethey are neutral in aqueous acid or basic
solutions. Because they are S or N containing compounds and therefore, have an atom with an unshared pair of electrons, they are expected to dissolve in concentrated H2SO4.
N They are insoluble in water due to the dominance of their non-polar groups. They are insoluble in 5% NaOH and in 5% HCl because they are neutral in aqueous acid or base solutions. However, they behave as base in more acidic solvents such as concentrated H2SO4, thus they are soluble in the latter.
I They are insoluble in water due to the dominance of their non-polar groups. They are insoluble in 5% NaOH and in 5% HCl because they are neutral in aqueous acid or base solutions. They are too weakly basic to dissolve in concentrated H2SO4.
EXPERIMENT 2 – RECRYSTALLIZATION AND MELTING POINT DETERMINATION OF BENZOIC ACID Factors to be considered in choosing recrystallization solvent
a. Soluble at high temperatures and sparingly soluble at room temperature
b. Impurities insoluble with solvent both at high temperature and low temperature c. No reaction between solvent and solute
d. Solvent is moderately volatile
e. Boiling point of solvent should be less than the melting point of solute f. Solvent is inexpensive, nonflammable and nontoxic
Crude BA with water Saturated solution Heat the mixture Increase solubility
Add animal charcoal colored compounds/impurities are adsorbed to the surface Hot filtration prevention of premature recrystallization
Prevention of premature recrystallization:
- Fluted paper – larger surface area faster filtration - Short stemmed funnel
- Pre-heat receiving flask
- Add small amount of hot solvent
Supersaturated seeding of pure BA; scratching the side of the glass Unsaturated boil off excess solvent
Cool in ice bath aid formation of crystals by decreasing solubility Filter and wash with cold solvent wash off mother liquor in the crystal % Recovery and Melting Point: Sharp, ±2°C
EXPERIMENT 3 PURIFICATION OF CRUDE BENZOIC ACID BY SUBLIMATION Sublimation – solid to liquid
Deposition – gas to solid
Requirement for sublimation to occur:
- Compound has high vapor pressure at temperature below melting point of the compound so that your compound will not pass through liquid phase.
Limitation:
- Not all solid compounds can satisfy this condition therefore they cannot be purified by sublimation
- Low percent yield Boiling point of BA : 122°C
Parameter Recrystallization Sublimation
Procedure Tedious
Involves many steps Simple and easy One step
Percent Yield High yield Low yield
Purity Low purity
Wide range of MP High purity ~100% Sharp of MP (±2°C)
EXPERIMENT 4 – LIQUID PHASE CHROMATOGRAPHY Paper Chromatography
- Stationary phase - Mobile Phase
Liquid (H2O at the surface of cellulose) – Liquid (chromatographic solvent) TLC
Solid (silica gel) – Liquid (chromatographic solvent) Retardation factor/Retention Factor = Dsolute/Dsolvent
Normal phase – stationary phase – polar (H2O)
Solvent polarity – relatively silica gel is nonpolar Polarity of highest spot – nonpolar
Polarity of lowest spot – polar Reversed phase – stationary phase – nonpolar
Polarity of highest spot – polar Polarity of lowest spot – nonpolar UV – 254 nm – conjugated compounds 365 nm – fluorescent compounds TLC Silica gel 1. H2SO4 ∆H 2. pH indicator
2-dimensional technique – separate second spot
EXPERIMENT 5 – ISOMERISM AND STEREOCHEMISTRY
Isomers – compound of the same molecular formula but different structures Two types of Isomers
1. Structural Isomers/Constitutional Isomers Ethanol and dimethyl ether
CH3-CH2-OH and CH3-O-CH3
They differ in the order atoms are bonded together
2. Stereoisomers – atoms are bonded in the same order but they differ in the orientation of atoms in space; usually drawn with wedges and
a. Conformational isomers (single bonds) – interconvertible rotation about a single bond; characterized by torsional angle
o Newman projection (staggered, eclipsed, anti, gauche)
b. Geometric isomers (double bonds)– cis-/trans-; E/Z conformations
o Determine priority group attached to each carbon by the Cahn-Ingold-Prelog rule c. Optical Isomers (chiral carbon) – has the ability to rotate plane-polarized light
o Enantiomers – non superimposable mirror image Determine absolute configuration
Find the chiral carbon (four different group attached) Assign priorities by Cahn-Ingold-Prelog rule
Look at the molecule to the bond of lowest priority group and chiral carbon Counterclockwise – S; Clockwise – R
o Mesocompound – contain chiral centers but is superimposable mirror image (2S, 3R) (2R, 3S)
EXPERIMENT 6 SYNTHESIS OF ALKYL HALIDES 1. Mechanism:
3.
Nucleophilc Substitution - Sn1 –unimolecular - Sn2 – bimolecular
Dependent only in the concentration of ions Conditions for Sn2 to occur:
1. Solvent – should be polar, protic (with H+), ionic (as much as possible)
In this reaction the solvent is HCl because it reacts immediately with tert-butyl alcohol.
2. Substrate – stable carbocation
Rate depends on the stability of the carbocation Allylic bezylic > 3° > 2° > 1° > -CH3
Methodology
t-butanol + cold conc. HCl in excess
Cold – to slow down the reaction and no avoid volatilization
In excess – to ensure that the reaction will proceed and to prevent formation of side products
Side products:
a. di-tert-butylether
b. 2-methylpropene
+ NaCl (sat’d) – salting out saturation Allow mixture to stand
Discard aqueous (bottom)
+ solid NaHCO3 until no more effervescence – to remove water + anhydrous CaCl3 – to further remove water
+boiling chips – aid boiling. Indirectly increase temperature Perform distillation
Collect in ice bath
First drop signifies the experimental boiling point of the product EXPERIMENT 7 – ALCOHOLS, PHENOLS, ETHERS
1. Lucas Test
o reagent is acidic, protonating –OH group, forming a carbocation o Zn2+ is a lewis acid (e- acceptor); makes alcohol a better living group o reagent is polar-ionic, favoring carbocation function
false positive result: benzyl alcohol o not very soluble in Lucas reagent
o test relies on solubility difference between alcohol and alkyl chloride only alcohols with 5 C or less can be reacted with Lucas reagent
2. Oxidation of Alcohols Neutral KMnO4
Oxidation is only possible for primary and secondary alcohols 1° alcohols carboxylic acid
2° alcohols ketone
*Benzyl alcohol acts like 1° alcohols
*Ethers – inert to oxidation by KMnO4 and H2CrO4 3. Acidity of phenols
o presence of electron withdrawing groups (EWGs) results to stability of conjugated base (phenoxide)
o ↑ EWG, ↑ resonance, ↑ stability of phenoxide, ↑ acidity pH
Phenol 5
p-nitrophenol 3 Picric acid 1
4. Complexation of Phenols with FeCl3
-products depend on the conjugating group present
Bright colors (characteristics of complexes) 5. Reaction of Phenol with Br2
o EAS electron aromatic substitution
6. Oxidation of Phenols
- Produces quinones unsaturated ketones
EXPERIMENT 8 and 9 – ALIPHATIC AND AROMATIC HYDROCARBONS and RELATIVE RATES OF ELECTROPHILIC AROMATIC SUBSTITUTION
Saturated Aliphatic Hydrocarbons – Hexane – single bonds and C and H - Inert, insoluble in cold concentrated H2SO4
Unsaturated Aliphatic Hydrocarbons – Limonene - Generally undergo addition reactions - Soluble in cold concentrated H2SO4 Aromatic Hydrocarbons – Benzene
- Generally undergo substitution
- Insoluble in cold concentrated H2SO4 but soluble in fuming H2SO4 Electrophilic Aromatic Substitution
*electrophilic should be very reactive
*An EDG can facilitate EAS (it stabilizes cationic intermediate)
1. Cationic intermediate forms aromacity is temporarily lost ∴ stability ↓
∴ EDG stabilizes the intermediate *presence of EDG
*stable intermediate *rate of reaction
EDG – o-p directors (o-p position where the charge is) - -OH, -NH, -NHR, -NR2 strong
- -OR, -NHCOR moderate - C6H5, R weak EWG – m-directors
- -NO2, -NR2+, -CX3 strongly deactivating
- -CN, -COOH, -COOR, -CHO, -COR, CONH2, SO3H weakly deactivating Some EWG are o-p-directors
- -F, -Cl, -Br, -I deactivating 2. Aromatic Bromination
Performed in dark conditions to avoid other reactions involving bromine and to ensure only electrophilc aromatic substitution will take place
Aniline > phenol > acetanilide > p-nitrophenol > benzene > chlorobenzene 3. Effect of solvent
- Solvent should be a Lewis acid (AlCl3/FeCl3) or a polarizing solvent
Unsaturated Aliphatic Hydrocarbons
Distillation – purification technique used for liquid mixtures
Simple distillation – used for separation of liquids whose boiling point differ greatly Steam distillation – used for separation of liquids that are heat sensitive
Tert-butyl chloride
White and orange positive for benzene Friedel-crafts alkylation
Test for aromatic ring
In the experiment
Bromine in light conditions
Hexane and limonene positive results - Alkanes
- Rate depends on stability of free radical intermediate Benzylic acid > 3° > 2° > 1° > methyl
Br—Br 2Br initiation H3C—H + Br CH3 + HBr propagation Br—Br + CH3 CH3Br + Br propagation CH3 + CH3 CH3CH3 termination Br—Br Br2 termination Br + CH3 CH3Br termination *limonene contains alkane group as well
Br2 in dark
Test for unsaturation Electrophilic addition
Does not work in aromatic because they are stable Beyer’s Test (inconclusive test)
Test for unsaturation Oxidation
Combustion Flame test
Alkane: 2 C6H14 + 19 O2 12 CO2 + 7 H2O
Alkene: C10H16 + 14 O2 8 C + CO + CO2 + 8 H2O Aromatic: C6H6 + 3 O2 3 C + CO + CO2 + 3 H2O
