Hey there! Sign in to join this conversationNew here? Join for free

Azo dyes synthesis question Watch

Announcements
    • Thread Starter
    Offline

    2
    ReputationRep:
    "Outline how you could carry out reaction III in the lab starting with phenol and a suitable aromatic amine."

    What I've done:

    C6H5NH2 + HNO2 + HCl ---> (<10degreesC) C6H5N2+Cl- (those are charges, ie the diazonium ion) + 2H2O

    Then Ive done C6H5N2+Cl- + C6H5OH + NaOH --->(NaOH(aq)) C6H5N=NC6H5OH + NaCl + H2O

    (Ive done it all in skeletal formulae for the aromatics)

    This is copied from the book

    The mark scheme says:

    "Add phenylamine to sodium nitrate and HCl below 10degreesC . Add the product to an alkaline solution of phenol.

    Surely it's better to write phenylamine + HNO2...and if the MS insists, do the reaction for HNO2 seperately...NaNO2 + HCl --> HNO2 + NaCl ?

    If im wrong pelase say..just the mark scheme seems a bit crap in this question =/

    These are the questions in the OCR A A2 textbook, with the MS from the Exam Cafe CD

    Please help!
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by Chemhistorian)
    "Outline how you could carry out reaction III in the lab starting with phenol and a suitable aromatic amine."

    What I've done:

    C6H5NH2 + HNO2 + HCl ---> (<10degreesC) C6H5N2+Cl- (those are charges, ie the diazonium ion) + 2H2O

    Then Ive done C6H5N2+Cl- + C6H5OH + NaOH --->(NaOH(aq)) C6H5N=NC6H5OH + NaCl + H2O

    (Ive done it all in skeletal formulae for the aromatics)

    This is copied from the book

    The mark scheme says:

    "Add phenylamine to sodium nitrate and HCl below 10degreesC . Add the product to an alkaline solution of phenol.

    Surely it's better to write phenylamine + HNO2...and if the MS insists, do the reaction for HNO2 seperately...NaNO2 + HCl --> HNO2 + NaCl ?

    If im wrong pelase say..just the mark scheme seems a bit crap in this question =/

    These are the questions in the OCR A A2 textbook, with the MS from the Exam Cafe CD

    Please help!
    The issue here is that nitrous acid cannot be stored and must be prepared 'in situ' as it spontaneously decomposes at RT.

    You should always use sodium nitrite (not nitrate) and dilute HCl below 10ºC

    NaNO2 + HCl --> HONO + NaCl
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by charco)
    The issue here is that nitrous acid cannot be stored and must be prepared 'in situ' as it spontaneously decomposes at RT.

    You should always use sodium nitrite (not nitrate) and dilute HCl below 10ºC

    NaNO2 + HCl --> HONO + NaCl
    Thanks What does 'in situ' mean?
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by Chemhistorian)
    Thanks What does 'in situ' mean?
    It means that I'm showing off my fluent Latin skills ...

    It's a phrase which is used when you make something 'in the same place' as you are carrying out the reaction, usually because the reactant is unstable (eg HONO) or simply difficult to obtain.

    For example, when you're reacting alcohols with phosphorus tribromide (which is not particularly nice to handle or easy to get hold of) you add phosphorus and bromine, which first react together 'in situ' to make the PBr3, which then can go on and brominate the alcohol.

    R-OH ----- (P + Br2) ---> R-Br
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by charco)
    It means that I'm showing off my fluent Latin skills ...

    It's a phrase which is used when you make something 'in the same place' as you are carrying out the reaction, usually because the reactant is unstable (eg HONO) or simply difficult to obtain.

    For example, when you're reacting alcohols with phosphorus tribromide (which is not particularly nice to handle or easy to get hold of) you add phosphorus and bromine, which first react together 'in situ' to make the PBr3, which then can go on and brominate the alcohol.

    R-OH ----- (P + Br2) ---> R-Br
    Thanks What's the difference in the whole ite ate thing? like sulphite/sulphate and nitric and nitrous acid?

    Thanks
    Offline

    2
    ReputationRep:
    the oxidation state of the nitrogen or phosphorus changes due to the differing amount of oxygen attached to it.

    NO2- = Nitrite (III), NO3- = Nitrate (V)
    SO32- = Sulphite (IV) , SO42- = Sulphate (VI)
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by gingerbreadman85)
    the oxidation state of the nitrogen or phosphorus changes due to the differing amount of oxygen attached to it.

    NO2- = Nitrite (III), NO3- = Nitrate (V)
    SO32- = Sulphite (IV) , SO42- = Sulphate (VI)
    How come both the charges are the same even though there are different amounts of oxygen?

    ie NO2- and NO3- ?

    Thanks
    Offline

    17
    ReputationRep:
    (Original post by Chemhistorian)
    How come both the charges are the same even though there are different amounts of oxygen?

    ie NO2- and NO3- ?

    Thanks
    the non-oxygen atoms in the ions have different oxidation states, like in iron (II) oxide, FeO, and iron (III) oxide, Fe2O3
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Will you be richer or poorer than your parents?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.