EDITORIAL

Chemical Pathways: 150 Years of Evolution of Chemistry

Laurence Lestel[a] and Igor Tkatchenko[b]

In 1857, a small group of chemists began to meet for informaldiscussions in Paris, founding the Societe Chimique. Takingnote of its national stature, the society was transformed intothe “Societe Chimique de France” in 1906.Then, after having merged with the “Societe deChimie Physique”, it became the “Societe Fran-caise de Chimie” in 1984. It celebrates its 150th

anniversary this year. The “Societe” witnessedthe evolution of chemistry and chemists, of theirknowledge, and of their goals, as did the otherchemical societies created in this era, for ex-ample, the Chemical Society of London in1841, the German Chemical Society in 1867,the Russian Chemical Society in 1868, theAmerican Chemical Society in 1876 or theChemical Society of Japan in 1878. Can one ina few words seize the impact of these changes?

In 1857, organic synthesis was still in its in-fancy. Berthelot achieved the formation of fatsby the combination of glycerol with acids in1854. In addition his syntheses of organic com-pounds by means of simple chemical methods,

Marcellin Berthelotsuch as those used at that time for inorganicderivatives in the famous “electric egg” appar-atus, led to the final fall of the theory of a “vitalforce” inherent in organic compounds. His book“Chimie Organique Fondee sur la Synthese”(1860) had considerable success and presentsBerthelot as the founder of this discipline. Atthe same time, Perkin deposited his patent“Dyeing fabrics” (1856) in England, describinghow to obtain dyes starting from residues of thedistillation of coal, and this opened the way forthe dye industry. After having deposited 152 pat-ents to cover the development of the industrialprocess, BASF began the production of indigo

Charles Friedel

in 1897. In these crucial years, the structures that allowed thedevelopment of the organic chemical industry fell into place:chemical companies (BASF, Hoechst, Bayer, Ciba, Geigy,

[a] Dr. L. LestelConservatoire National des Arts et Metiers C.D.H.T.E.,5 rue du Vertbois, 75003 Paris, FranceE-mail: lestel@cnam.fr

[b] Dr. I. TkatchenkoCNRS-U. Bourgogne/ICM/SymCat,9 ave Alain Savary, 21078 Dijon Cedex, FranceE-mail: tkatchen@u-bourgogne.fr

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British Alizarin, les Usines du Rhone, ...), industrial researchlaboratories associated to academic research, and new develop-ments in chemistry such as chemical engineering, a term that

was introduced in England in 1887 by Davisand rose to greater recognition at MIT, ex-panded rapidly as a required step for industrialscale-up. After having used “simple” reactionslike nitration, reduction or oxidation of organicmolecules, chemists started to use reactionsspecific to organic chemistry, for example,preparation of zinc alkyl iodides by Franklandfor hydrocarbon synthesis, the Williamson syn-thesis for the preparation of ethers, and the useof sodium for the condensation of alkyl or arylhalides by Wurtz and then by Fittig. In 1877,Friedel and Crafts used anhydrous aluminumchloride as catalysts for the condensation ofaromatic hydrocarbons and alkyl halides. TheFriedel�Crafts reaction was applied to thepreparation of perfumes, pharmaceutical prod-ucts, dyes, and then monomers. It is essential tothe chemical industry still today, albeit in moreeco-compatible forms. A few years later, theGrignard reaction (1900), which allows the for-mation of a wide variety of organic compoundsby the reaction of magnesium with organic iod-ides, was acquainted with a singular develop-ment, unique in the history of chemistry. An-other useful tool was the hydrogenation of olef-ins by using catalysts as studied by Sabatier andSenderens. Progress in organic chemistry wasaccompanied by the set-up of its nomenclatureduring the congress of Geneva in April 1892,after two years of work by the Parisian com-mission of nomenclature chaired by Friedel.

Then a competition started between nature andartifice, between products resulting from nature and those imit-ating it or exceeding it. To understand the structure of naturalproducts, the chemist decomposed them into small units, andthen tried their synthesis. The apotheosis is the total synthesisof vitamin B12, undertaken by Woodward and his team in Har-vard, in collaboration with Eschenmoser of Zürich. More than100 researchers, including Lehn, took part in it. It was com-pleted in eleven years and was announced in Delhi in 1972.

To fight against the shortage of resources and to improve pro-ductivity, the chemist found new synthetic routes (e.g. sodium

carbonate by the Solvay process; ammonia through hydrogen-ation of nitrogen; hydrocarbons and methanol starting fromcoal). The list is endless. It widened with the isolation of fluor-ine by Moissan, the discovery of rare gases by Ramsay, andthe disclosure of radio elements by the Curie family.

The chemist also created completely new entities, for ex-ample, macromolecules. Polymer chemistry took off in the1920s with Staudinger, who led the scientific community inthe synthesis of long chain polymers, the physicochemicalproperties of which were intriguing for a longtime and began to be explained with the softmatter concepts of de Gennes. The understand-ing of the organization of soft matter thanks toa large variety of weak interactions betweenmolecules, not atoms, led to the design of nu-merous new man-made materials with improvedperformances, or “smart” materials mimickingnatural ones. This was further extended to thearea of liquid crystals, which are essential com-ponents of our everyday life. The design of new

Marie Curiesynthetic strategies and their industrial achieve-ment allowed the development of alternatives topolymeric natural products like silk (Nylon) andrubber (polychloroprene, polybutadiene, poly-isoprene, ...). Moreover, new materials appearedwith the design of polyesters and polyolefinsstarting from C2�C6 building blocks obtainedfrom petroleum cuts. Such developments dem-onstrate again the continuum existing betweenbasic research and industrial processes: the bestexample is certainly the discovery of theZiegler�Natta catalysts, which have heavilycontributed to the rise of the petrochemical Pierre-Gilles de Gennesindustry.

The development in the second half of the 19th

century of terrestrial (railways, metallicbridges) and maritime communications (andalso armament) triggered the progress of metal-lurgy. Bessemer, Thomas, Siemens, and Martindesigned new processes to obtain steels fromcast iron; Hall and Heroult patented the elec-trolysis of alumina and the arc furnace. A scien-tific vision of industry is also shown by manycontributions from Le Chatelier, professor atCollege de France then at Sorbonne, both in thefields of metallurgy and cements. Although Jean Rouxel

used in the Neolithic era, ceramics were madein a much more rational manner, leading to a broad diversityof properties and applications. A better understanding of thesematerials, in which defects are, at the same time, a major dis-advantage and a source of original behavior, led to solid-statechemistry, which appeared as a mature discipline at a Bor-deaux congress held in 1964. From “hard”, “shake and bake”chemistry, it became a tailored, “soft” chemistry, thanks, inparticular, to the work of Rouxel and Livage, who approachedthis new world either with the chemical treatment of preformedmaterials or the stepwise and controlled synthesis from molec-

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ular species in solution. Again, natural structures and syntheticproducts are intrinsically linked through replication of con-structions like the silica architectures of diatoma! A comp-lementary approach relates to microporous materials, sourcesof “shape-selective” catalysts, membranes, and, even in its lat-est achievements, traps and reservoirs for molecular species.

The identification of new sources of natural products thathave astonishing structures with an impressive number of chi-ral centers shows the immense diversity of the molecular, mac-

romolecular, and inorganic structures. An Alsa-tian, Werner, by proposing spatial arrangementsof molecular entities around a metal cation todescribe coordination complexes, laid the foun-dations of organization at a supramolecular le-vel. Another Alsatian, Lehn, developed thisconcept, leading in a rational way to supramol-ecular chemistry with auto-organization andthen self-assembly of increasingly complexentities. Nature, while being based on the multi-plicity of ion�ion, ion�molecule, and mol-ecule�molecule interaction modes, exploits thisconcept with increasing complexity, leading fi-nally to living organisms capable of self-repli-cation. Supramolecular chemistry suggests thatif these interactions can be broken in the sameway as they are made, a genuine constitutionaldynamic chemistry would be in operation, pro-viding original structures capable of auto-repair,another property related to all living things.

Many of these developments would not havetaken place if the structure of the organic mole-cule had not been understood. In 1858, Kekuleproposed to describe organic molecules by theircarbonaceous sequence, the carbon atom beingtetravalent. The same year, Couper, who workedin the Wurtz laboratory in Paris, presented at theyoung “Societe Chimique de Paris” his ideas onthe “forces of attraction” that exist between thevarious elements of an organic molecule, whatwe call now bonds between atoms. The Couperformulae were used by Meyer in Germany, thenby Boutleroff in France, who proposed the term“chemical structure” in 1864 “to indicate thechemical sequence or the way in which theatoms are connected” in a molecule. In the sameyear, modern chemical writing was introduced,thanks to Brown who depicted the atoms by

their symbols and each connection by a continuous line. In1874, the tetrahedral image of carbon was proposed by van’tHoff and Le Bel, hence opening the way to the three-dimen-sional representations of organic molecules. Thus, we canunderstand why apparently identical molecules are in fact dis-symmetrical and deflect light differently. If “only the productsborn under the influence of Life are dissymmetrical”, then “allthe molecules prepared in our laboratories are symmetrical”,said Pasteur. However, in 1894, Fischer, who studied the ster-eospecificity of enzymes, deduced from his observations the

EDITORIALstructural “key�lock” relationship between a sugar and its en-zyme. Prelog, Kagan, and many others used all the subtletyof asymmetric synthesis, then of enantioselective catalysis, toobtain man-made optically active compounds.

We have such a clear vision of atoms in our mind that wemay have forgotten how strong the opposition was to atoms inFrance during the 19th century. At that time, atoms were atheoretical concept introduced by Dalton at the beginning ofthe 19th century, and this concept was adoptedby the whole chemistry community during theKarlsruhe meeting in September 1860. In 1877,the Academy of Sciences was the witness of aviolent controversy between Berthelot, opposedto, and Wurtz, defender of atomism. Wurtz andhis many students employed the “Societe Chi-mique de Paris” and its Bulletin as a mightyplace for defending atomism in France, whichgradually enabled the conversion of Frenchchemists to this theory. Bohr applied the quan-

Jean-Marie Lehntum theory to the planetary model of the atomproposed by Rutherford in 1911. To describechemical bonding Lewis and Kossel developed,in 1916, the octet relationship, based upon theouter electrons. Hückel in Germany and Mul-liken in the United States introduced molecularorbitals; however, Pauling is the true holder ofthis new approach, by introducing the notion ofhybridization of carbon orbitals in a paper is-sued in 1931, and by publishing his famousbook: “The Nature of the Chemical Bond” in1939. If this era represents the golden age ofthe covalent bond, then other interactions were Louis Pasteuralready taken into account: from dative bonds,first introduced by Werner, to the generalizationof Lewis interactions, to weaker interactionslike van der Waals forces present in soft matter.The importance of the hydrogen bond, exem-plified by Pimentel’s work, strongly contributedto the understanding of interactions occurring inbiological systems: let us recall that the DNAstructure is controlled by hydrogen bonds,which are also present in supramolecular chem-istry. In addition to this diversity of bondingmodes, the introduction of new concepts and

Henry Le Chatelierthe improvement of mathematical methods anddata-processing led to descriptive and predictivetools for these connections and the resulting properties. Fortyyears after the foundations were set down by Schrödinger, thework of Hartree and Fock, Kohn and Pople have providedtools like density functional theory (DFT), now unavoidablefor the understanding of physical and chemical properties.

Parallel to the development of this writing that makes chemis-try a science which has its own alphabet, the desire of compre-hension of the chemical reactivity was also very strong. Fol-lowing the seminal works of Carnot, Kelvin, and Clausius, thedevelopment of thermodynamics led to the birth of physical

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chemistry — a junction of chemistry and physics — exem-plified by Le Chatelier, Gibbs, Arrhenius, van’t Hoff, andOstwald, who often were chemists as much as they were physi-cists: Didn’t Ostwald develop the ammonia oxidation process?It is worth noting the subtle differences that have appearedsince between physical chemistry and chemical physics, if oneconsiders the microscopic and now nanoscopic domains atwhich new chemical reactivity is being born. Physical chemis-try, like analytical sciences, irrigates all the disciplines of

chemistry, and the younger generations oftenneglect its importance; it is, for example, behindthe classification of fundamental reactions oforganic chemistry established by Ingold!

All these advancements could not have beendone without a panoply of analytical tools push-ing back the limits of detection and temporalscales of observation for more than two centur-ies. Centesimal analysis introduced after theworks of Lavoisier and Priestley by Gay-Lussacand Thenard, Berzelius, Dumas, Liebig, andPregl, to quote only the major contributors, wassupplemented by isotopic analysis and determi-nation of exact masses by high-resolution massspectrometry. Separative analysis experiencedextraordinary developments following the in-vention of chromatography by Tswett, a Rus-sian botanist with a predestined name. If we hadto wait until 1931 for the work of Kuhn on theseparation of carotenes, then the post-war per-iod saw the systematic recourse to this tech-nique and its numerous alternatives, crowned bythe Nobel Prize of Sanger in 1958. The pharma-ceutical industry even exploits Tswett’s tech-nique to obtain optically active molecules fromracemates.

Emission and absorption spectroscopy can beapplied to an extremely broad frequency range,providing information on the structure and themovement of the chemical objects. This devel-opment goes hand in hand with a growing mas-tery of technology: in 1939, Beckmann intro-duced the first UV/Vis spectrophotometer,which enabled Woodward to achieve his PhDwithin one year � the first of the Woodwardrules. The advancement of mass spectrometryled to considerable achievements as a spin off

of the Manhattan project. In the same way, the rise in the useof increasingly high radio frequencies and intense magneticfields benefited resonance spectroscopy, leading to the emerg-ence, for example, of 1 GHz NMR spectrometers able to solvethe structure of proteins of several tens of thousands of daltons.Lastly, the current data-processing resources has made it pos-sible to systematize the use of Fourier transform with respectto NMR, IR, and EPR spectroscopy, mass spectrometry, andso forth. The discovery of X-rays on the eve of the 20th centuryhas also contributed to the knowledge of the crystalline struc-ture of increasingly complex molecules. In fact, the develop-

ment of intense and focused sources (synchrotron radiation),two-dimensional detectors (a consequence of Charpak’s work),and powerful computational tools supplements the spectro-scopic studies of molecules and macromolecules.

As never satisfied, the chemist also seeks todirectly see the object of his studies. The devel-opment of magnetic lenses has allowed the vis-ualization of nanometric and sub-nanometricobjects by electron microscopy. Scanning elec-tron microscopy is of primary importance forthe development of materials and the study oftheir behavior. A new stage was reached withthe work of Rohrer and Binning on scanningtunnelling microscopy (STM) and its deriva-tives, which allows not only the observation at

Joseph Fourieratomic scale, but also writing on this scale withatoms. The last achievement in microscopytechniques, recently developed by Zewail, takesadvantage of laser coherent electron packets generated withfemtosecond laser pulses. The combination of spatial and tem-poral dimensions makes possible the analysis of the dynamicstructure of inorganic, organic, and biological materials with-out damaging the objects by high-resolution electron mi-croscopy.

This extraordinary rise in laser technology largely opened thefield of the studies including time as the fourth dimension in

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chemistry. The exploration of the “Femtoland” by Zewail,associated to the modeling of the processes studied, offersextraordinary prospects for the comprehension of chemical re-

activity. Other methodologies, with other time-scales, also make it possible to access varioustypes of chemical events. Thus, cyclic voltam-metry at very high scanning rates contributesto the mechanistic studies of electroactivesystems; synchrotron radiation allows time-resolved diffraction experiments, and so forth.

Will we attend the birth of a virtual chemis-try? It should be hoped that it does nothing butsupplement the pallet of chemistry now ex-tending to constitutional dynamic chemistry. Toreturn to Berthelot, in conclusion, let us recallhis remark: “the chemist creates the object ofhis study”. The objects become only more com-plex and offer a promising future to chemistryand to chemists.

AcknowledgmentsWe wish to acknowledge the members of Club d’Histoire de la Chimieand the writers of numerous biographies of former presidents of the“Societe Francaise de Chimie”.