Topic 9 Nitrogen compounds Revision Notes

Transcription

1 Tpic 9 Nitrgen cmpunds Revisin Ntes 1) Amines - intrductin In primary amines, a nitrgen atm is attached t ne alkyl grup and tw hydrgen atms. The general frmula fr a primary amine is RNH2 The simplest amine is methylamine, CH3NH2. Other amines f interest are ethylamine, CH3CH2NH2, and phenylamine, C6H5NH2 In amines, the N has 3 bnding pairs and 1 lne pair s shape is pyramidal, bnd angle = 107 2) Amines as bases Bases are prtn (H + ) acceptrs. Amines can accept prtns because f the lne pair n the N This lne pair frms a c-rdinate bnd with an H + e.g. with an acid CH3NH2 + HCl CH3NH3 + + Cl - Methylamine methylammnium chlride with water CH3CH2NH2 + H2O CH3CH2NH3 + + OH - Ethylamine ethylammnium hydrxide N nw has 4 bnding pairs s its shape is tetrahedral, bnd angle ) Preparatin f amines a) Reductin f nitrbenzene t make phenylamine Here, reductin means gain f hydrgen C6H5NO2 + 6[H] Nitrbenzene C6H5NH2 + 2H2O phenylamine Cnditins Tin (Sn) and cncentrated hydrchlric acid Reflux b) Substitutin f halgenalkanes CH3CH2Cl + NH3 Chlrethane CH3CH2NH2 + HCl ethylamine Cnditins excess ammnia disslved in ethanl

2 4) Synthesis f az dyes Az dyes cntain the az functinal grup -N=N- Az dyes are brightly clured and bnd well t fabrics Phenylamine can be cnverted int an az dye by a tw stage prcess Stage 1 phenylamine t diaznium salt C6H5NH2 + HNO2 + HCl Phenylamine C6H5N N + + Cl - + 2H2O benzenediaznium chlride Cnditins HNO2/HCl (nitrus acid/hcl) r NaNO2/HCl (sdium nitrite/hcl) <10 C (t prevent the diaznium salt decmpsing) Stage 2 cupling with phenl under alkaline cnditins C6H5N N + + C6H5OH + OH - C6H5N=NC6H4OH + H2O Cnditins phenl/naoh <10 C These reactins are used in frmatin f dyestuffs (sluble substances used fr staining r cluring fabrics) 5) Amin acids - intrductin Amin acids fund in living things have the general frmula RCH(NH2)COOH where R is an alkyl grup Amin acids cntain an acidic functinal grup (-COOH) and a basic functinal grup (-NH2). This means they can act as bth acids and bases (they are amphteric) Technically, these are -amin acids because the NH2 is n the C next t the COOH. -amin acids have the -NH2 n the next but ne C t the COOH If R is H, the amin acid is glycine, NH2CH2COOH. The prper chemical name fr glycine is 2-aminethanic acid If R is CH3, the amin acid is alanine, CH3CH(NH2)COOH. The prper chemical name fr glycine is 2-aminprpanic acid All amin acids, apart frm glycine, shw ptical ismerism as the central C has fur different grups attached t it

3 There are 20 different amin acids in the human bdy

4 6) Effect f ph At a ph value called the iselectric pint, amin acids exist as zwitter ins (zwitter is a German wrd whse English equivalent is hybrid). These ins cntain a full psitive charge and a full negative charge The COOH has lst H + and the NH2 has gained H + Amin acids exist in this frm in the slid state and have high melting pints because there are strng in-in frces between the zwitter ins Different R grups in α-amin acids result in different iselectric pints At a ph lwer than the iselectric pint the amin acid has the frm shwn belw. The amin acid is in acidic cnditins and the NH2 will gain H + t becme NH3 + At a ph higher than the iselectric pint the amin acid has the frm shwn belw. The amin acid is in alkaline cnditins and the COOH will lse H + t becme COO - 7) Dipeptides, plypeptides and prteins Amin acids can jin tgether t frm dipeptides This uses the COOH grup f ne amin acid and the NH2 grup f anther amin acid (see equatin n next page) The link between the tw amin acids is called a peptide link (-CONH-) This is a cndensatin reactin (a small mlecule, like water, is prduced when a link is made) Three amin acids jined tgether make a tripeptide. Several amin acids in a chain are a plypeptide Prteins are lng chains f amin acids. Prtein chains are held in ne f tw basic shapes by hydrgen bnds between the N-H f ne amin acid and the C=O f anther amin acid

5 If the 2 amin acids are nt the same, 2 different dipeptides can be frmed e.g. HOOC-CHR 1 -NHCO-CHR 2 -NH2 R 1 nearest COOH HOOC-CHR 2 -NHCO-CHR 1 -NH2 R 1 nearest NH2 A peptide link can be split up by hydrlysis Acid hydrlysis with HCl(aq) prduces amin acids (COOH grups) Alkaline hydrlysis with NaOH(aq) prduces carbxylates (COO - grups)