El­e­ments Mat­ter

Ni­tro­gen – The life-es­sen­tial el­e­ment Veena Pat­ward­han - Spe­cial Cor­re­spon­dent

Chemical Industry Digest - - What’s In? - Veena Pat­ward­han, Spe­cial Cor­re­spon­dent

Ni­tro­gen is a cru­cial, life-sup­port­ing sub­stance. It is a part of DNA – our ge­netic code, and is found in many bi­o­log­i­cally sig­nif­i­cant mol­e­cules. Read on to know more about this colour­less, odour­less gas, that makes up 78% of the at­mo­spheric air.

Much like Oxy­gen and Car­bon, the seventh el­e­ment of the pe­ri­odic ta­ble – Ni­tro­gen – is also a cru­cial, life­sup­port­ing sub­stance. Ni­tro­gen is a part of our DNA – our ge­netic code. It’s a con­stituent of sev­eral bi­o­log­i­cally sig­nif­i­cant mol­e­cules such as haem (in haemoglobin) and acetyl­choline (the neu­ro­trans­mit­ter in the ner­vous sys­tem of hu­mans and other life forms). It is also the vi­tal build­ing block of amino acids that form proteins, and en­zymes. It is present in our bones, blood, and tis­sues, con­sti­tut­ing around 3% of the mass of the hu­man body.

But not just for hu­mans, ni­tro­gen is es­sen­tial for the sur­vival, growth, and sus­te­nance of all liv­ing things. In short, all life on earth needs ni­tro­gen.

A colour­less, odour­less, non-toxic, di­atomic gas that makes up around 78% of the air around us, Ni­tro­gen is also the most abun­dantly avail­able pure el­e­ment on earth. How­ever, should its con­cen­tra­tion in the at­mos­phere rise way above its present lev­els, we would all suf­fo­cate to death.

What’s in a sci­en­tific name?

By the eigh­teenth cen­tury, fol­low­ing in­ves­ti­ga­tions by Carl Wil­helm Scheele, Henry Cavendish, and Joseph Pri­est­ley, sci­en­tists be­lieved that there were two kinds of ‘airs’ – ‘fire air’ or de­phlo­gis­ti­cated air that sup­ported com­bus­tion (and that we now know as oxy­gen), and a ‘foul air’ (mostly ni­tro­gen mixed with a small quan­tity of car­bon diox­ide, though they didn’t know this then) that was left be­hind once the ‘fire air’ was con­sumed. In 1772, a young Scot­tish chemist and botanist, Daniel Rutherford, car­ried out ex­per­i­ments to get rid of both oxy­gen and car­bon diox­ide from the air, and found that what re­mained con­tained what he called ‘nox­ious’ air or ‘phlo­gis­ti­cated’ air. He pub­lished his find­ings in his doc­toral the­sis sug­gest­ing that air mostly con­sisted of this nox­ious gas. We now know his con­clu­sions about the gas he had dis­cov­ered were wrong, but since he was the first to pub­lish his find­ings about ni­tro­gen, he is cred­ited with hav­ing dis­cov­ered the gas.

The French sci­en­tist Lavoisier sug­gested the newly

> The French sci­en­tist Chap­tal came up with the name ‘ni­trogène’ (ni­tro­gen) de­rived from the Greek words ‘nitron’ and ‘genes’ that to­gether meant ‘ni­tre form­ing’, ni­tre be­ing the old name for Potas­sium Ni­trate from which Cavendish had suc­cess­fully pro­duced the gas. And that’s how Ni­tro­gen got its cur­rent English name.

dis­cov­ered gas be given the name ‘azote’ which he had de­rived from the Greek word ‘azotikos’ mean­ing ‘no life’. He picked the name based on the fact that the gas was mephitic since an­i­mals placed in an at­mos­phere that was purely made up of this gas died of as­phyx­i­a­tion. English sci­en­tists pointed out that with the ex­cep­tion of oxy­gen, al­most all gases were mephitic and so re­jected Lavoisier’s sug­ges­tion. Ger­man sci­en­tists pro­posed the name ‘stick­stoff’ de­rived from the Ger­man words ‘er­stricken’ (mean­ing suf­fo­cat­ing) and ‘stoff’ (mean­ing sub­stance). But, English sci­en­tists ob­jected to this name as well. Then the French sci­en­tist Chap­tal came up with the name ‘ni­trogène’ (ni­tro­gen) de­rived from the Greek words ‘nitron’ and ‘genes’ that to­gether meant ‘ni­tre form­ing’, ni­tre be­ing the old name for Potas­sium Ni­trate from which Cavendish had suc­cess­fully pro­duced the gas. And that’s how Ni­tro­gen got its cur­rent English name. In­ter­est­ingly how­ever, the French de­cided they pre­ferred the name ‘azote’, while the Ger­mans have stuck to ‘stick­stoff’! And in English, some ni­tro­gen com­pounds are in­deed based on Lavoisier’s name and called azides and azo com­pounds.

Am­mo­nia, one of the most abun­dant ni­tro­gen-con­tain­ing com­pounds in the at­mos­phere, got its name from Am­mon – a pow­er­ful de­ity of an­cient Egypt, near whose tem­ple large salt de­posits con­tain­ing am­mo­nium chlo­ride used to be found. Am­mo­nium chlo­ride it­self was called Sal am­mo­niac mean­ing salt of Am­mon.

The most abun­dantly used in­dus­trial gas

Ni­tro­gen is pro­duced by dis­till­ing liq­uid air. Around 45 mil­lion tonnes of ni­tro­gen are pro­duced this way each year to meet the de­mands of a wide range of in­dus­tries. Be­ing in­ert, gaseous ni­tro­gen is com­monly used for pro­vid­ing an un­re­ac­tive at­mos­phere for pro­tect­ing re­ac­tive ma­te­ri­als from com­ing in con­tact with oxy­gen, for pre­serv­ing food items, and also in the elec­tron­ics in­dus­try dur­ing the pro­duc­tion of tran­sis­tors and diodes. An­neal­ing of stain­less steel is also car­ried out in an at­mos­phere of ni­tro­gen gas.

Liq­uid ni­tro­gen is ben­e­fi­cial be­cause of its cold­ness and in­ert­ness as well and is com­monly used as a re­frig­er­ant. It is used for pre­serv­ing sperm, eggs, and other cells for med­i­cal re­search and re­pro­duc­tive tech­nol­ogy, for per­form­ing cryo­genic surgery dur­ing which un­wanted tis­sue is cut off by freez­ing it to very low tem­per­a­tures, and for rapidly freez­ing foods so they can main­tain their mois­ture, taste, colour, and tex­ture.

Chem­i­cals, phar­ma­ceu­ti­cals, glass and ce­ram­ics, petroleum, pulp and pa­per, health­care, steel, and metal re­fin­ing and fabrication are some of the many in­dus­tries that use ni­tro­gen in large quan­ti­ties. Ni­tro­gen is also a key feed­stock for the chem­i­cal in­dus­try, used for man­u­fac­tur­ing hun­dreds of chem­i­cal com­pounds for di­verse in­dus­tries such as fer­tilis­ers, food, phar­ma­ceu­ti­cals, ny­lon, dyes and ex­plo­sives, au­to­mo­biles, etc.

But be­fore it can be con­verted to dif­fer­ent chem­i­cals, ni­tro­gen must first be re­acted with hy­dro­gen to pro­duce am­mo­nia. To­day, the Haber-Bosch process is the most eco­nom­i­cal artificial ni­tro­gen fix­a­tion process used in­dus­tri­ally, in­volv­ing the syn­the­sis of am­mo­nia from ni­tro­gen and hy­dro­gen. Around 210 mil­lion tonnes of am­mo­nia is man­u­fac­tured each year us­ing this process. It is first con­verted to ni­tric acid and there­after to var­i­ous other chem­i­cals. But, am­mo­nia is mainly used as a fer­tiliser, be­ing ap­plied di­rectly to the soil or in the form of am­mo­nium salts.

The Ni­tro­gen Cy­cle and Ni­tro­gen Pol­lu­tion

Most of the atoms of ni­tro­gen in the at­mos­phere ex­ist as N – as a pair bound to­gether by a pow­er­ful tri

2 ple bond, too pow­er­ful for liv­ing or­gan­isms to break. To get ac­cess to ni­tro­gen for their sus­te­nance, plants and an­i­mals there­fore need it to be in a re­ac­tive ‘fixed’ form, to be ‘fixed’ to el­e­ments like car­bon, hy­dro­gen, or oxy­gen mostly as or­ganic ni­tro­gen com­pounds. The bi­o­log­i­cal process of fix­ing at­mo­spheric ni­tro­gen by con­vert­ing it into am­mo­nia is car­ried out by soil bac­te­ria. Other bac­te­ria like the ones that live sym­bi­ot­i­cally in­side nod­ules on the roots of plants such as beans and peas, con­vert the am­mo­nia into com­plex ni­tro­gen com­pounds like

> The other source of nat­u­rally oc­cur­ring re­ac­tive ni­tro­gen is due to light­ning. The en­ergy it gen­er­ates con­verts oxy­gen and ni­tro­gen to ni­tric ox­ide (NO). This is ox­i­dised to ni­tro­gen diox­ide (NO ), and then to ni­tric 2 acid that is car­ried from the at­mos­phere to the ground by rain, snow, or other forms of de­po­si­tion. Light­ning plays an im­por­tant role in ni­tro­gen fix­a­tion in ar­eas where there’s a scarcity of ni­tro­gen-fix­ing plants.

amino acids and proteins.

The other source of nat­u­rally oc­cur­ring re­ac­tive ni­tro­gen is due to light­ning. The en­ergy it gen­er­ates con­verts oxy­gen and ni­tro­gen to ni­tric ox­ide (NO). This is ox­i­dised to ni­tro­gen diox­ide (NO ), and then to ni­tric

2 acid that is car­ried from the at­mos­phere to the ground by rain, snow, or other forms of de­po­si­tion. Light­ning plays an im­por­tant role in ni­tro­gen fix­a­tion in ar­eas where there’s a scarcity of ni­tro­gen-fix­ing plants.

‘Ni­tro­gen fix­a­tion’ is ac­tu­ally Na­ture’s way of pre­par­ing fer­tilis­ers in the soil for nur­tur­ing plants di­rectly and all life on earth in­di­rectly. Plants are the first to feed on the ni­tro­gen com­pounds. An­i­mals get their re­quire­ment of th­ese by feed­ing on plants. And then hu­mans get theirs from the plants and an­i­mals they eat. Ni­tro­gen com­pounds re­turn to the soil in the form of hu­man and an­i­mal waste prod­ucts. Bac­te­ria in the soil then con­vert th­ese ni­tro­gen com­pounds back to ni­tro­gen gas, which is re­leased into the at­mos­phere.

Since long now, to feed a rapidly grow­ing world pop­u­la­tion, crop yields are be­ing boosted by adding fer­tilis­ers to the soil. How­ever, ex­ces­sive use of fer­tilis­ers in agri­cul­ture de­stroys soil health rather than mak­ing it more fer­tile, be­sides ad­versely af­fect­ing the en­vi­ron­ment, aquatic life, and hu­man health as well. The ex­cess fer­tiliser is con­verted by soil bac­te­ria into ni­trates that then get leached into the ground wa­ter or get washed out of the soil into rivers and lakes. Al­gae in the wa­ter bod­ies feed on the ni­trates and grow rapidly, re­duc­ing the oxy­gen avail­able in the wa­ter for aquatic flora and fauna. The pol­lu­tion of ground and sur­face wa­ter leads to do­mes­tic wa­ter sup­ply too, hav­ing danger­ously high ni­trate lev­els. Con­sum­ing fer­tiliser-pol­luted wa­ter causes var­i­ous types of can­cer, re­pro­duc­tive prob­lems, hy­per­ten­sion, and ‘blue baby dis­ease’ in in­fants. Ba­bies fed for­mula pre­pared with ni­trate-rich wa­ter, de­velop a blue-grey coloura­tion of the skin due to de­creased oxy­gena­tion of their blood.

Overuse of fer­tilis­ers also re­sults in in­creased ni­tro­gen emis­sions such as am­mo­nia, ni­tro­gen ox­ide, and ni­trous ox­ides. Th­ese ni­troge­nous gases lead to res­pi­ra­tory prob­lems in hu­mans, and also play a prom­i­nent role in global cli­mate change, ni­trous ox­ide be­ing one of the more po­tent green­house gases.

But, de­spite its dis­as­trous con­se­quences, ni­tro­gen pol­lu­tion is not get­ting as much at­ten­tion as car­bon pol­lu­tion. It is es­ti­mated that in Europe alone, the en­vi­ron­men­tal and hu­man health costs of ni­tro­gen pol­lu­tion could be around €70-320 bil­lion per year. The ni­trate lev­els in the wa­ter­ways of most in­dus­tri­alised na­tions are on the rise. In the rivers in the north­east­ern United States and many coun­tries in Europe, ni­trate con­cen­tra­tions have in­creased 10 to 15 times in the last 100 years. Also, Oxy­gen-starved ar­eas or ‘dead zones’ have been found in the Gulf of Mexico, the Baltic Sea, the Adri­atic Sea, the Gulf of Thai­land, the Yel­low Sea, and the Ch­e­sa­peake Bay.

Re­duc­ing our ni­tro­gen foot­print

Clearly, it’s now time to take a closer look at our ni­tro­gen foot­print too, that is, the amount of ni­tro­gen re­leased into the en­vi­ron­ment by dif­fer­ent hu­man ac­tiv­i­ties. The best part is that re­duc­ing our ni­tro­gen foot­print will also re­duce our car­bon foot­print. Ac­cord­ing to many ex­perts, the so­lu­tion to curb­ing the ex­ces­sive use of ni­tro­gen fer­tilis­ers could be sus­tain­able agri­cul­ture, pop­u­lar­i­sa­tion of or­ganic farm­ing, and ed­u­cat­ing farm­ers about the en­vi­ron­men­tal is­sues aris­ing out of un­con­trolled use of fer­tilis­ers.

Ref­er­ences

1. Agata Blaszczak-Boxe: Facts about Ni­tro­gen – LiveS­cience. com, 27 Septem­ber, 2017, https://www.lives­cience. com/28726-ni­tro­gen.html

2. R. Thomas San­der­son: Ni­tro­gen – En­cy­clopae­dia Bri­tan­nica, 27 April, 2018, https://www.bri­tan­nica.com/sci­ence/ni­tro­gen

3. John Em­s­ley: Na­ture’s Build­ing Blocks: An A-Z Guide to the El­e­ments – Ox­ford Univer­sity Press, 2011

4. Uni­ver­sal In­dus­trial Gases Inc: Ni­tro­gen (N2) Prop­er­ties, Uses and Ap­pli­ca­tions – Ni­tro­gen Gas and Liq­uid Ni­tro­gen – http://www.uigi.com/ni­tro­gen.html

5. Royal So­ci­ety of Chem­istry: Pe­ri­odic Ta­ble – Ni­tro­gen – http://www.rsc.org/pe­ri­odic-ta­ble/el­e­ment/7/ni­tro­gen

6. Yale Univer­sity: The world’s ni­tro­gen fix­a­tion, ex­plained – Sci­enceDaily, 23 Septem­ber 2015, www.sci­encedaily.com/ re­leases/2015/09/150923133513.htm

7. Ee Ling Ng, Deli Chen, Robert Edis: Ni­tro­gen pol­lu­tion: the for­got­ten el­e­ment of cli­mate change – The Con­ver­sa­tion, 5 De­cem­ber, 2016.

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