An Introduction to Phosphorus: History, Production, and Application

JOM, Jun 2007 by Gleason, William

When it was discovered in 1669, phosphorus became a wonder of the European courts and fairs, with the chemilumine scent combination of phosphorus and atmospheric oxygen producing a light show no one had ever seen before or even thought possible. Within ten years of its discovery, a new curiosity emerged when Robert Boyle improved the production method by adding SiO^sub 2^ to the mix, then coating paper with the resulting phosphorus. When he drew a wood splinter through the paper, it lit on fire. From that essential function of providing instant fire, phosphorus eventually found other uses, including fertilizer and detergents. Today, very few smelters of any capacity remain, with the greatest production volume coming from China.

INTRODUCTION

Phosphorus, number 15 in the periodic table, is a non-metallic element with a density of 1.8 g/cm^sup 3^ and an atomic volume of 17cm^sup 3^/mol.1 It was discovered and named in 1669 by the Hamburg merchant and alchemist Hennig Brandt when he heated powdered charcoal and evaporated urine residues.2

Brandt's method is shown in Reactions 1 and 2:

(NH^sub 4^)NaHPO^sub 4^ [arrow right]NaPO^sub 3^ NH^sub 3^ H2O (1)

8NaPO^sub 3^ 10C [arrow right]2Na^sub 4^P^sub 2^O^sub 7^ 1OCO P^sub 4^ (2)

The condensed vapor from this reaction was a waxy solid that glowed in the dark but gave off no heat. He named the substance after Venus, the morning star, using the Greek form of phosphorus instead of the Latin form, Lucifer, which was probably a wise choice given the political climate of the time. It fast became a wonder of the European courts and fairs,3 with the chemiluminescent combination of phosphorus and atmospheric oxygen producing a light show no one had ever seen before or for that matter even thought possible. Keep in mind that at the time, only naturally occurring elements such as gold and copper were generally known. Zinc had been produced in India for possibly two millennia, but in Europe, only Albertus Magnus had intentionally isolated arsenic by an artificial process. A glow-inthe-dark, artificially created material then was not only profoundly unique but bordered on magical.

HISTORY OF PHOSPHORUS: MAGICAL AND DEADLY

The element itself has neighbors of nitrogen, arsenic, silicon, and sulfur but has little in common with them. Phosphorus does not easily give up electrons, so it is not found as a cation, has only one stable isotope of P^sup 31^, forms both a P^sub 2^ and a P^sub 4^ molecule, and commonly exhibits a valence of 3 or -3 but can make use of all five available electrons for covalent bonding. Many of its compounds are complex, bordering even on the strange, so the study of this element is most interesting, not to mention potentially deadly. Although there are several allotropes, the two principle forms are red and white, sometimes referred to as yellow because many times the white form has a thin skin of the red form, giving it a yellowish tinge. The white form generally exists as tetrahedral P4 molecules that change to P^sub 2^ molecules at high temperature. The red form, made by heating at 200-300°C in a retort with air excluded, retains the tetrahedral form but turns amorphous, displaying a longterm, polymeric structure.1 The white form is the waxy solid so popular in seventeenth century shows and is extremely toxic. While the fatal dose is considered to be 150 mg, the U.S. National Institute for Occupational Safety and Health determined 5 mg/m3 to be "immediately dangerous to life or health." Death has been reported from a dose as small as 1 mg/kg.4 All these amounts are small enough to make one wonder how many of those alchemists died an early death because of it.

Within ten years of its discovery, a new curiosity emerged when Robert Boyle (of Boyle's law fame) improved the production method by adding SiO^sub 2^ to the mix, then coating paper with the resulting phosphorus. When he drew a wood splinter through the paper, it lit on fire.5 The improved curiosity show drew rave reviews, but the cost and difficulty of producing phosphorus kept it an expensive curiosity.

Boyle's production method is shown in Reaction 3:

4NaPO^sub 3^ 2SiO^sub 2^ 10C [arrow right] 2Na^sub 2^SiO^sub 3^ 10CO P^sub 4^ (3)

In 1830, the French chemist Charles Sauria reformulated Walker and Jones' vile smelling "Lucifer" match using white phosphorus. Times had changed enough so the Latin form of the word was now acceptable, but white phosphorus was still lethal, and people still died from it. One pack of the matches had enough phosphorus to kill an adult, but no matter how many children sucked on the things and were poisoned, the astounding convenience of fire on demand still sold matches. The means of producing the white phosphorus for these matches was not only dangerous but very expensive, with bone ash and hydrochloric acid precipitating phosphates, then this mix being treated for days in a sealed, coal-heated crucible, then transferred to a retort with final distilling under water. 6