Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it.  CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃ coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄ into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄ into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.

Fundamentals of thermodynamics:- 1st law, 2nd law and 3rd law short notes

·         Deals with energy and the energy changes.

Thermodynamics can only give information about a system when it is at equilibrium state; a time-invariant state.

When it is based on the concept of equilibrium it’s known as “Equilibrium thermodynamics”.

When it is based on the concept of time-invariant state it’s known as “Thermodynamics of Steady state” or “non-equilibrium thermodynamics”.

Equilibrium thermodynamics: - Only with closed and isolated systems.

System

·         Open: Both matter and energy can transfer between system and surroundings.

·         Closed: Only energy can transfer.

·         Isolated: Neither energy nor matter can transfer.

·         Homogenous system: Consists of a single phase.

·         Heterogeneous system: Consist of two or more phases.

Isothermal: Constant T

Isobaric: Constant P

Isochoric: Constant V

Adiabatic: No heat transfer between the system and the surroundings.

Heat and work do not belong to system and are NOT properties of thermodynamics.

They are operations which performed on the system to alter its energy.

Properties

·         Extensive: Describe and depend on the size of the system. (Mass, volume, pressure…)

·         Intensive: Does not depend on the size of the system. (Molar volume, Molecular weight, Temperature…)

First law

Introduces the concept of internal energy.

·         DQ = U + W

From 1^st law;

When isothermal: DU= 0

                              DQ = DW

At constant volume: DW = 0

                                  DQ = DU

W = - PDV   it is a minus value for a closed system in expansion

W=nRTln.V_f / V_i   Can be taken for an isothermal expansion of a gas

Heat capacity

C=dQ/dT

At constant P: C_p= (dH/dT)_p

At constant V: C_v= (dU/dT)_v

To know how the reaction proceeds we need to know;

·         Enthalpy-H

·         Entropy-S

Enthalpy

DH^o  = å n H^o_products  - å n H^o_reactants

DH = U + PV

DH = C_pdT (as above mentioned in heat capacity)

DH = mCDǾ

Second Law

Describes entropy. Entropy is an idea of randomness in a reaction.

S>0 reaction is spontaneous

S<0 reaction is non spontaneous

S=0 reaction is at equilibrium

·         DS  =  DQ/T

At constant pressure

DS  =  DH/T

Also;

DS_universe  =  DS_system  +  DS_surroundings

DS^o  =  å n S^o_products  -  å n S^o_reactants

Third law

Absolute Entropy, S, =  0  at 0  Kelvins for a perfect crystal of a pure substance.

DG,  Gibbs Free Energy

The maximum amount of energy available to do useful work on the surroundings.

·         DG  = D H – T D S

DG  <  0  (-) Spontaneous

DG  >  0 (+) Spontaneous in the opposite direction       DG  =  0  equilibrium

·         DG^o  =   DH^o  -  T DS^o

DS (+), DH (-) Spontaneous at all temperature

DS (+), DH (+) Spontaneous at high temperatures (where exothermicity is relatively unimportant)     

    

DS (-), DH (-) Spontaneous at low temperatures

            (where exothermicity is dominant)

DS(-), DH (+)  Process not spontaneous at any temperature (reverse process is spontaneous at all temperatures)

·         DG  = DG^o  +  RT ln Q

                       Q  =  Reaction Quotient.

Free energy at equilibrium

·         G  =  0

·         So DG^o  =  -RT ln Q_equilibrium

              Q_equiliibrium  =  K_p (gases)

                                 =  K_c  (solution)

Preparation of Sodium Carbonate extract - Identify Sulfates, Nitrites, Nitrates and Phosphates by using the prepared Sodium carbonate solution

Preparation of Sodium Carbonate extract

200mg of the unknown sample, 1g of Na₂CO₃ and 50ml of distilled water was added into a clean dry flask later boiled using a tripod stand. This was done by clamping a funnel above the flask to reduce evaporation.

It was boiled for about 5 minutes.

Afterwards solution was cooled and filtered using a filter paper.

A colorless filtrate was obtained.

Identify Sulfates, Nitrites, Nitrates and Phosphates by using the prepared Sodium carbonate solution

SO₄^2-

Procedure	Observation
5 drops of Na2CO3 extract was acidified with dil. HCl in boiling tube. Acidity was checked with litmus. It was kept in a hot water bath for about 3 minutes and added 3 drops of BaCl2	When the extract was acidified with HCl, it turned into brownish red colour. White colour precipitate was formed.

NO₂^-

Procedure	Observation
1ml of Na2CO3 extract was heated with dil. H2SO4 in boiling tube. The evolved gas was checked with starch.iodide paper.	With H2SO4 the extract turned into reddish brown colour. Brown fume was evolved when heating. It turned the starch-iodide paper into blue colour.

NO₃^-

Procedure	Observation
1ml of Na2CO3 extract was heated with 100mg Sulphamic acid in a boiling tube. Later dil.NaOH was added and heated until the evolution of NH3 is ceased. It was again checked with Devarda’s alloy.	In the presence of Sulphamic acid the solution turned into brownish red. Pungent smelling brownish colour gas was formed and the it continued for awhile in Devarda’s alloy.

PO₄^3-

Procedure	Observation
1ml of Na2CO3 extract, 1ml of dil. HNO3 and 10ml ammonium molybdate was heated gently in a boiling tube.	With HNO3 the extract turned into brownish red colour. Later a yellow colour precipitate was obtained.

What’s the purpose of preparing Na₂CO₃ extract?

It gives an expedient way of bringing all the anions of the sample into solution. Otherwise they might be insoluble and couldn’t carry out the experiment properly. Also it prevents the cation in interfering.

What is the importance of Na₂CO₃ extract to be clear and colourless?

This provides a better setting to observe formations of precipitates, colour changes which take place during the experiment.

Is the Na₂CO₃ extract basic or acidic?

It is slightly basic.

Basis of biochemical tests; Biuret test, Benedict test, Iodine/potassium iodide test, Emulsion test

Biuret test
A test for peptide bonds to identify proteins.

In the presence of dil.copper sulphate in alkaline solution, nitrogen atoms in the peptide chain form a purple complex with copper(ll) ions. Biuret is a compound derived from urea which also contains the –CONH- group and  gives a positive result.

Benedict test

A test for sugar

Reducing sugars- Benedict’s solution contains copper sulphate. Reducing sugars reduce soluble blue copper sulphate. Here the containing copper(ll) ions will change to insoluble red- brown copper oxide containing copper(l). This is seen as the precipitate.

Non-reducing sugars- The disaccharide will hydrolysed to its monosaccharide elements by boiling with dil. HCl. Such as Sucrose will be hydrolysed to glucose and fructose which are both reducing sugars. That will give the reducing sugar results with the Benedict’s test.

Iodine/potassium iodide test

A test for starch.

What is given at last is a poly-iodide complex formed with starch.

Emulsion test

A test for Lipids

Lipids are iinsoluble with water. Adding water to a solution of the lipid in alcohol results in an emulsion of lipid droplets or micelles in the water. These reflect light and give a white, opalescent appearance.

Tests for Phenols - Discussion

Phenol

Catechol

Resorcinol

2-napthol

Solubility

Some phenols (Ex: Phenol,catechol,resorcinol) are soluble in water and others are sparingly soluble or insoluble in water because of the increasing molecular weight and hydrophobic nature. But all the phenols are capable of reacting with NaOH solution and dissolve.

C₆H₅OH + NaOH ----> C₆H₅ONa + H₂O

Reaction with Sodium carbonate

Phenols give no reaction with sodium carbonate but as the aqueous solution of it was used,phenols dissolved in it giving the same colourations given when testing the solubility in water.As Phenols do not produce gas from sodium carbonate it should be a very weak acid.

Benzoylation

To react with benzoyl chloride, phenol should be modified to make the reaction possible.the -COCl group is bounded directly to the benzene ring. Therefore it's less reactive.phenol is first dissolved in NaOH in order to get the phenoxide. Later it's reacted with the Benzoyl chloride.

Tests for Carboxylic acid - Discussion

Acetic acid

Benzoic acid

Salicylic acid

 Cinnamic acid

Solubility
Acetic acid is soluble in water but Benzoic acid,salicylic acid and cinnamic acid are insoluble due to their heavy molecular weight and increased hydrophobic nature. Carboxylic acids are acidic therefore they can dissolve in bases such as ethanol and sodium hydroxide forming the carboxylate ion/salt.


Reaction with Sodium carbonate
Reacts with sodium carbonate liberating carbon dioxide

Esterification
Acetic acid----> Medicinal or strong odour of apples
Benzoic acid----> Fruity odour
Salicylic acid----> Medicinal odour
Reaction with Ferric chloride
Higher acidity can interfere the final results. Therefore it's important to use neutral ferric chloride neutralized by sodium hydroxide.
FeCl₃ + C₆H₅COO^-   -------->     Fe ( OOC₆H₅)₃
FeCl₃ + CH₃COO^-   -------->     Fe ( OOCH₃)₃
Cinnamic acid with KMnO4
This will give out Benzaldehyde and acetic acid. Almond odour was given due to the formation of benzaldehyde.