Alwin Kloekhort’s 2007 dissertation from Leiden University, “The Hittite Inherited Lexicon,” is openly available online via Leiden University’s scholarly repository. Per the project’s abstract,
In over 1200 pages this dissertation describes the history of Hittite in the light of its Indo-European origin.… Part One, ‘Towards a Hittite Historical Grammar’, contains a description of the Hittite phoneme inventory and a discussion of the sound laws and morphological changes that have taken place between the Proto-Indo-European and the Hittite language stage. Part Two, ‘An Etymological Dictionary of the Hittite Inherited Lexicon’, contains etymological treatments of all Hittite words of Indo-European origin. One of the most important conclusions of this dissertation is that the Anatolian language group was the first one to split off from Proto-Indo-European and that all other Indo-European branches have undergone a period of common innovations. Therewith Anatolian, and especially Hittite, occupies a very important position within comparative Indo-European linguistics as it sometimes has retained linguistic information that has been lost in all other Indo-European languages.