Today in Science History – January 19 – Carl Gräbe and Benzene Nomenclature


Carl Gräbe

Carl Gräbe (1841 – 1927)

January 20 marks the passing of Carl Gräbe. Gräbe was a German organic chemist who discovered a method to synthesize the distinctive red alizarin dye with Carl Liebermann. Alizarin red has been a color found in textiles dating back to the Pharaohs of Egypt. This color was produced from the flowering plant called madder. Madder grows all around the “Old World” regions of Asia, Africa, and Europe. Even though this plant grows nearly everywhere, it took a lot of madder to make even a little bit of dye. Gräbe and Liebermann isolated the compound responsible for the red coloring in madder and developed a method to artificially synthesize the alizarin compound from anthracene. This made the dye significantly less expensive and started a boom in artificial dye development in the textile and chemical industries.

Gräbe was also the chemist who introduced the nomenclature used to describe bond locations on benzene rings. Benzene is a ring of carbon atoms forming a hexagon. When two functional groups attach themselves to different points of the hexagon, different prefixes are used to differentiate different patterns. There are three different ways two functional groups can connect to the carbon atoms of the benzene ring. The first is the two are opposite each other. The second is where a gap of one carbon atom between them and the third is when they are attached to neighboring carbon atoms. Gräbe introduced the use of the prefixes para-, meta-, and ortho- to distinguish between these arrangements. Para- is added to the name the first grouping, meta- is the prefix for the second, and ortho for the third.

Take the compound xylene. Xylene is a compound with a benzene ring and two methyl groups (-CH3) attached.

xylene configurations

Three different configurations of xylene.

This is one of the simplest ways to visualize Gräbe’s contribution to organic chemistry nomenclature.

Notable Science History Events for January 19

2006 – NASA launches New Horizons mission to Pluto.

New Horizons Spacecraft

New Horizons Spacecraft
NASA

NASA launched their New Horizons spacecraft on a flyby mission to the dwarf planet, Pluto. It arrived in 2015 and became the first man-made object to visit Pluto. It began transmitting pictures and data back to Earth as it approached and passed Pluto. It sent its last image in October 2016 and began its trip to the Kuiper Belt. It is expected to reach its first Kuiper object early 2019.

1927 – Carl Gräbe died.

1878 – Henri-Victor Regnault died.

Henri Victor Regnault

Henri Victor Regnault (1810 – 1878)

Regnault was a French physical chemist who researched the properties of gases. He proved that Boyle’s law only applied to ideal gases and approximated real gases. He made many precise measurements of the specific heats of several solids, liquids and gases and coefficients of thermal expansion of several gases. He also showed no two gases had the same coefficient of expansion.

1826 – Johann Elert Bode was born.

Johann Elert Bode

Johann Elert Bode (1747 – 1826)

Bode was a German astronomer who determined the orbit of Uranus. He is also known for his empirical law to determine the distances of the planets from the Sun. To use Bode’s law, start with the sequence 0, 3, 6, 12, 24, etc. where each number after 3 is twice the previous number. Add 4 to each number and divide the result by 10. The resulting first six numbers of the sequence are 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, and 10.0. These values closely approximate the distances in astronomical units of the planets from the Sun.

1813 – Henry Bessemer was born.

Henry Bessemer

Henry Bessemer (1813-1898)

Bessemer was an English inventor who developed an inexpensive steel manufacturing process. The Bessemer process involves blowing oxygen through the molten iron to burn off impurities. This process greatly boosted the use of steel in manufacturing and structural engineering.

He was a prolific inventor who held over 100 patents. He also made a substantial amount of money exploiting many of his inventions. 

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